It's a bit of a misnomer.

All TVS diodes conduct in both directions.

The difference is:

• Unidirectional TVS

It's like a high current, low capacitance, high pulse power Zener diode: in the forward direction, it's a diode, so it will conduct at the usual diode threshold voltage. In the reverse direction, it will conduct only when voltage exceeds the rated breakdown voltage. It is meant to protect signal voltages of only one polarity (usually positive, like your USB lines). It is wired in the circuit in reverse bias, like a Zener diode, so it limits voltage between -0.6V and the breakdown voltage. This is what you need for USB or the usual logic signals which are always positive or zero volts.

• Bidirectional TVS

It's like two of the above in series, back to back, so it will conduct in any direction if breakdown voltage is exceeded. This is meant to protect signals which can go positive and negative, for example analog signals like audio. It will limit voltage between negative breakdown voltage and positive breakdown voltage.

To select the diode for 5V, consider:

• It must not conduct at 5V ("standoff voltage")

• It must conduct at a voltage that is below the absolute maximum rating input voltage of the LDO that will follow ("breakdown voltage", pay attention to the current it is specified at)

• For a power supply, capacitance is not important

So don't just type "5V TVS" in the search engine, you have to read the link at the beginning of this answer and select the proper part.

It's a bit of a misnomer.

All TVS diodes conduct in both directions.

The difference is:

• Unidirectional TVS:

  It's like a high current, low capacitance, high pulse power Zener diode: in the forward direction, it's a diode, so it will conduct at the usual diode threshold voltage. In the reverse direction, it will conduct only when voltage exceeds the rated breakdown voltage. It is meant to protect signal voltages of only one polarity (usually positive, like your USB lines). It is wired in the circuit in reverse bias, like a Zener diode, so it limits voltage between -0.6V and the breakdown voltage. This is what you need for USB or the usual logic signals which are always positive or zero volts.

• Bidirectional TVS:

  It's like two of the above in series, back to back, so it will conduct in any direction if breakdown voltage is exceeded. This is meant to protect signals which can go positive and negative, for example analog signals like audio. It will limit voltage between negative breakdown voltage and positive breakdown voltage.

To select the diode for 5V, consider:

• It must not conduct at 5V ("standoff voltage")

• It must conduct at a voltage that is below the absolute maximum rating input voltage of the LDO that will follow ("breakdown voltage", pay attention to the current it is specified at)

• For a power supply, capacitance is not important

So don't just type "5V TVS" in the search engine, you have to read the link at the beginning of this answer and select the proper part.

It's a bit of a misnomer.

All TVS diodes conduct in both directions.

The difference is:

• Unidirectional TVS

It's like a high current, low capacitance, high pulse power Zener diode: in the forward direction, it's a diode, so it will conduct at the usual diode threshold voltage. In the reverse direction, it will conduct only when voltage exceeds the rated breakdown voltage. It is meant to protect signal voltages of only one polarity (usually positive, like your USB lines). It is wired in the circuit in reverse bias, like a Zener diode, so it limits voltage between -0.6V and the breakdown voltage. This is what you need for USB or the usual logic signals which are always positive or zero volts.

• Bidirectional TVS

It's like two of the above in series, back to back, so it will conduct in any direction if breakdown voltage is exceeded. This is meant to protect signals which can go positive and negative, for example analog signals like audio. It will limit voltage between negative breakdown voltage and positive breakdown voltage.

To select the diode for 5V, consider:

• It must not conduct at 5V.

• It must conduct at a voltage that is below the absolute maximum rating input voltage of the LDO that will follow.

• For a power supply, capacitance is not important

So don't just type "5V TVS" in the search engine, you have to read the link at the beginning of this answer and select the proper part.

It's a bit of a misnomer.

All TVS diodes conduct in both directions.

The difference is:

• Unidirectional TVS

It's like a high current, low capacitance, high pulse power Zener diode: in the forward direction, it's a diode, so it will conduct at the usual diode threshold voltage. In the reverse direction, it will conduct only when voltage exceeds the rated breakdown voltage. It is meant to protect signal voltages of only one polarity (usually positive, like your USB lines). It is wired in the circuit in reverse bias, like a Zener diode, so it limits voltage between -0.6V and the breakdown voltage. This is what you need for USB or the usual logic signals which are always positive or zero volts.

• Bidirectional TVS

It's like two of the above in series, back to back, so it will conduct in any direction if breakdown voltage is exceeded. This is meant to protect signals which can go positive and negative, for example analog signals like audio. It will limit voltage between negative breakdown voltage and positive breakdown voltage.

To select the diode for 5V, consider:

• It must not conduct at 5V ("standoff voltage")

• It must conduct at a voltage that is below the absolute maximum rating input voltage of the LDO that will follow ("breakdown voltage", pay attention to the current it is specified at)

• For a power supply, capacitance is not important

So don't just type "5V TVS" in the search engine, you have to read the link at the beginning of this answer and select the proper part.