What does "outdoors" mean?

1. (outside a building) outside in the open air, rather than inside a building.

Is it correct to say "We had an outdoors party."?

No — say "We had an outdoor party.". Use 'outdoor' (no -s) as an adjective before a noun. Use 'outdoors' as an adverb or noun.

outdoors

adv.

US //ˈaʊtˈdɔɹz// UK //aʊtdˈɔːz// out·doors

1 outside a building (adv.)
B1 Intermediate

outside in the open air, rather than inside a building.

in the open air; outside a house or building. This adverbial use is non-gradable and typically follows the verb.

Example

It was such a beautiful day that we decided to eat our lunch outdoors.

Example

The researchers spent the entire summer working outdoors, documenting the migration patterns of local bird species in their natural habitat.
- outside
- alfresco
- indoors
Pitfall

We had an outdoors party.

We had an outdoor party.

Use 'outdoor' (no -s) as an adjective before a noun. Use 'outdoors' as an adverb or noun.

Etymology 1

From out + doors (plural of door), probably as a shortening of out of doors. Alternatively, from outdoor (adjective) + -s (adverbial genitive suffix).

Etymology 2

From outdoor (verb) + -s (third-person singular suffix).