Pickup is one word when it functions as a noun or an adjective. It’s two words, pick up, when functioning as a verb. For example, you might drive your pickup to pick up your friend from a pickup football game, and congested traffic might make you late for the pickup.
Pick up is just one of hundreds of phrasal verbs that have one-word noun/adjective counterparts. For a few other examples, see runaway and run away, workout and work out, and payback and pay back. In informal use, the one-word forms often appear in place of the two-word forms, but the distinction is usually observed in edited writing, and the one-word forms never become standard as verbs.
Like many compounds formed from phrasal verbs, pickup is often spelled with a hyphen—pick-up—especially in varieties of English from outside North America, and some dictionaries list it this way. But most hyphenated compounds eventually lose the hyphen and become one word, and pickup is already widely treated this way.
New unemployment claims unexpectedly jumped last week, indicating a pickup in layoffs, a worrisome sign ahead of Friday’s important jobs report for May. [LA Times]
Employees typically have to travel to remote villages by motorbike or foot to pick up the goods that Arjuni sells. [New York Times]
The evening is drawing to a close and old Ben decides to impress Mme Lagarde with one of his stock pick-up lines. [Independent]
It’s a struggle to go pick up the essentials and be left with much change from a fifty these days. News.com.au]
Knowing his future was limited, Moore soon took delivery of a very special 1971 Cheyenne pickup truck. [National Post]