^Yep.
Basically when youre riding threaded forks, the top part of the headset is compression (locknut).
You can also use threaded forks with threadless headsets and use locknut as compression.
When youre riding threadless forks, you need compression and a threadless headset. There is 3 main compressions
HIC= Hidden internal compression. You need special HIC bars for this (oversized chromo bars). You need also a topcap, HIC shim, starnut and bolt. Install starnut into fork
SCS= Standard compression system. Compression inside of "quad clamp". You need SCS clamp, top cap, starnut and bolt. Install starnut into fork
ICS= Internal compression system. Long bolt and starnut that goes into bars. You dont need anything special. Might need top cap with some forks.
Compression systems prevent headset from wobbling.