The 74HC165 are 8-bit parallel-load or serial-in shift registers with complementary serial outputs (Q7 and Q7) available from the last stage.
When the parallel load (PL) input is LOW, parallel data from the D0 to D7 inputs are loaded into the register asynchronously.
When PL is HIGH, data enters the register serially at the DS input and shifts one place to the right (Q0 → Q1 → Q2, etc.) with each positive-going clock transition. This feature allows parallel-to-serial converter expansion by tying the Q7 output to the DS input of the succeeding stage.