Three networked computers

It means computers connected to each other: a network.

It can label IT work, a note about a home or office network (a LAN, local area network), or serve as a tidy bullet point in technical documents. It describes a setup, not a feeling, and it doesn't say whether the link is cabled, wireless or the internet; add a word when that matters.

Why does it look like an old office icon?

Because it comes from Microsoft's Wingdings picture font.

Wingdings, released in 1992 and developed from the Lucida Icons, Arrows and Stars fonts, turned small pictures of office and computer equipment into typeable characters. In 2014 Unicode 7.0 added many Wingdings pictures as real characters, this one among them, so it can now travel in any text instead of living only in that one font, though it still needs a font that has it to show up.