New member here
The website Erik posted looks like it has a ton of great info on harmony. So if you want a really thorough answer to your question I'd read that website and come back with any questions. Until then I can offer a (hopefully) shorter answer.
Harmony is the prevailing chord progression in a piece or a song. A chord the sounding of three or more notes simultaneously. In Wester classical and pop music, our harmony is based (largely) on Triads, three-note chords, and tertiary harmony (chords built in thirds). *Implied* harmony is when you don't have enough (usually 3) notes to definitively name the chords in a progression, but the lines of music do a fair job of letting you know what the chords are. Most bass lines, taken by themselves,
only ever imply harmony since chords that are more than 3 notes are slightly rare on basses. So almost any bass line you play is only going to imply the harmony of the song. It's usually, but not always, up to your guitarist, keyboard player, or whoever to actually fill the chords the rest of the way out.
Again, this is oversimplified but hopefully it's easier to digest than that website.