All 4 Uses

laboratory
in
We Beat the Street
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Rameck, you forgot that these lab reports must be turned in with writing only on the front of the paper.†
Chpt 11 *

lab = a workplace where people do scientific or medical research, or produce drugs or chemicals (also used figuratively) OR (as an adjective) related to such a place
None of them was aware that their futures were enclosed in a folder stuck between a peanut butter sandwich, a chemistry lab homework assignment, and a pair of dirty gym shoes.†
Chpt 12
Over the next few weeks, in between going to classes, studying for tests, and doing extensive work in lab classes, Rameck, George, and Sampson made the plans, found a faculty sponsor, and convinced the Student Government Association of the university to grant them permission to operate this new organization.†
Chpt 17
The rest of the students had had lots of prior experience in medicine and laboratory work.†
Chpt 21

Definitions:

(1) (laboratory)
a workplace where people do scientific or medical research, or produce drugs or chemicals

or (as an adjective): related to such a place
(2) (meaning too rare to warrant focus)
Much more rarely, lab can be used as an abbreviated way of saying Labrador retriever. It is also a rare last name and may indicate someone's initials.