"Bootstrapping" is a common technique in (analog) active filters, where the output of the filter is fed back to a node that would otherwise be connected to ground.
For example, the Sallen Key topology begins with two RC L-sections followed by a unity-gain buffer. Then the output of the buffer is also connected to the base of the first L-section (C3 in the following schematic). This is said to "bootstrap" that node.
Here is another example, from an old National Semiconductor app note, in which the ground node of a Twin-T notch filter is 'bootstrapped' in order to greatly increase the Q of the filter:
How can I understand the operation of the 'bootstrap' intuitively?