An adverbs describes a verb, an adjective or another adverb.
It gives us answers for questions like when, how, where, how often, how much, etc.
Example: How often does Lina goes to clinic? Seldom.
Where did you keep the glass? Inside the cupboard.
When are you going to meet him? I will be meeting him today.
Seldom, inside and today are an adverbs.