Cola vs. rabo

In the Spanish language, both 'cola' and 'rabo' can refer to the tail of an animal. However, these two words are not always used interchangeably.

Cola

'Cola' is a generic term for 'tail'. It is used to refer to the tail of any animal, bird or reptile.
El perro meneaba la cola.
(The dog was wagging its tail.)
La cola del pájaro es colorida.
(The bird's tail is colorful.)
El dragón tiene una cola muy larga.
(The dragon has a very long tail.)

Rabo

'Rabo' usually refers to long, thick or bushy tails, and it is typically used when referring to the tails of mammals. Moreover, 'rabo' can be colloquially used to refer to a certain body part in some regions, which makes its usage more limited.
El león movió su rabo.
(The lion moved its tail.)
El zorro sacudió su rabo.
(The fox shook its tail.)
El gato tiene un rabo esponjoso.
(The cat has a bushy tail.)

Summary

'Cola' and 'rabo' primarily differ in their usage nuances and can't always be used interchangeably. 'Cola' is a general term to denote the tail of any animal, bird or reptile, whereas 'rabo' often describes long, thick or bushy tails, especially those of mammals. The colloquial usage of 'rabo' can also make it less appropriate in certain contexts.