An Outpost is a manned base on Mars. However, it is not a settlement because the residents are only temporary.
Reason for an outpost
We need experience living on Mars before we can colonize. We also need a manned presence on Mars. We should setup an outpost on Mars before even the first people arrive. When the time for colonization is right, the outpost will develop into a fully fledged settlement.
Setup of an outpost
An outpost will be much like a semi-autonomous colony, albeit on a much smaller scale. Food, air, water and energy will be created in-situ. Crews could be replaced by a Manned Resupply mission