Figure 1. Tri-state buffers with opposite control logic. Image source.
It's a combination or overlay of the two symbols in Figure 1. Rotate the symbol on the right by 180° and overlay on the symbol on the left.
Figure 2. Borrowing the symbol from KingDuken's answer but changing the infill to show the two buffers.
If the control signal is high the gate transmits from left to right. If the control signal is low the gate transmits from right to left.
As the others have said, it is a transmission gate. To further explain, these transmission gates are driven by CMOS-based switches and they behave similarly to a relay.
Figure 1: Circuit equivalence and its symbol. Picture from Electronic-Tutorials.
It behaves very much so of a tristate buffer. Below is a truth table for such a device.
Table 1: Truth Table for Transmission Gate. Table is on the same page as the previous link.