I needed help with this one (thank you, /r/spiders!). At 2.5mm long, there weren’t a lot of details to go on! This petite lady is an adult female wall spider (Oecobius navus, very probably), and isn’t she darling? She’s sitting on my pillowcase, to give you a sense of scale.
Other than being tiny and hanging out on walls (or pillowcases), Oecobiidae can be identified by their legs — the front ones being twisted to point inwards at the “knees” and outwards at the “feet” (our little lady is kindly demonstrating the pose). Unlike most spiders, which have two pairs of legs pointing forward and two pairs pointing backward, Oecobiidae have all eight legs sticking straight out from their bodies in a starburst-like fashion.
The name Oecobiidae comes from the Greek words oikos (οικος), meaning “house”, and bios (βιος), meaning “living” — thus, these spiders are “living in the house”. As you may guess, these spiders are commonly found in human dwellings. Navus means “active” or “busy” — these spiders are very fast runners!
These are cribellate spiders, possessed of some nifty organs around the spinnerets. I really can’t do the description justice, so please see spiderbytes.org’s top-notch analysis (oh gawd) of the “incredible hairy butt” (“fringed anal tubercles” if you’re being all science-y) of Oecobius.
Other common names: baseboard spider, starlegged spider, disc web spider, dwarf round-headed spider, stucco spider. Also sometimes misidentified as Oecobius annulipes.