Who do te consider to be an animal "sidekick"?

I`ve just joined the club and I wonder who do te consider to be a "sidekick".
Is it just an animal character from a Disney movie who isn`t as major as the main animal character, right?
(Ok, maybe it sounds silly, but I`m just not sure. I`m going to make a pick but I don`t know who exactly is counted as a sidekick.)