“They're both avid travelers.”

You're talking with your roommate about a couple who you know well, but she doesn't know. They travel a lot, so you say:

They're both avid travelers.

(someone) is an avid (something)

When someone likes to do a certain activity a lot, you can describe them as "an avid ___".

You complete the phrase with a noun like "traveler": it's a label that describes the category of people who like to do that activity. Here are some other examples:

an avid reader

an avid fan

an avid gardener

an avid runner

The word "avid" sounds positive and intellectual.