Physics makes a distinction between these two words, but in non-physics contexts people don't usually need the distinction or can infer it from context, and thus those words are synonyms. Actually it's not uncommon for technical jargon to assign synonyms to similar concepts in a way that makes them not synonymous anymore.
Examples of speed and velocity as synonyms:
I ran around the block at a high velocity
I ran around the block at a high speed
If you were speaking informally, you could say either word and the sentence would mean the same thing to your listener (note: velocity sounds pretentious to me here). However technically once you've run around the block and returned to your starting point your net velocity is zero because your displacement is zero. A pedantic purist who would insist that "velocity" is incorrect in this sentence should assume that the speaker is simply referring to their instantaneous velocity and not their net velocity. Of course anything which has speed has velocity as well, but usually we just don't care about the direction part.
