Although both partner songs, and rounds/canons produce polyphonic texture, and both consist of two or more musical voices, there is an important difference between them:
Partner songs are different melodies performed at the same time.
Rounds and canons are identical melodies starting at different times.
Here is a short excerpt from a four-part round sung by a children's choir. Notice that all four musical voices contain the same melody, but they enter at different times. Click the play arrow to hear this example.
The example below shows another four-part round. Again, each voice enters separately with the same melody, but this time each voice repeats the melody once. Rounds are often performed this way. Notice that when all four voices have entered, the texture is so thick that it is difficult to distinguish among them as the melody is repeated. At the end you will hear the voices finish and drop out in the same sequence as they entered. Click the play arrow to hear this example.