A heroic couplet consists of two rhyming lines of verse with five iambic feet.
The word couplet refers to two lines - a couple means two. Iamb means that there are two syllables involved - the first syllable is unstressed, and the second one is stressed. Finally, heroic couplets are written in pentameters, which means they have 5 meters/feet, and each meter has 2 syllables, so there are 10 syllables in total in each line.
An example would be:
Then share thy pain, allow that sad relief;
Ah, more than share it, give me all thy grief