When talking about remote work, there often needs to be distinction between companies acting remotely, and companies who do the "traditional" way of working from a centralized office.
Co-Location means that people are in the same location or office. A co-located team or company is working with all (or at least most) team members from the location, office or even room. It is therefore the opposite of a distributed or remote company, where team members work from different locations.
Most types of work and teams nowadays are co-located.