A pleonasm is the use of more words than necessary to express an idea. In the case of two consecutive words meaning the same thing, it's a specific type of pleonasm called tautology.
For example:
* "He went back home." (Home implies going back)
* "It is very unique." (Unique already implies something is rare and special)
While pleonasms can be used for emphasis or stylistic effect, they are often considered redundant and can be edited out of writing.