IAW
In Accordance With. IAW means an action should be performed according to a stated requirement, manual, procedure, or instruction.
Expanded explanation
IAW ties the task back to a governing source
IAW appears across maintenance, compliance, and operational documents when the writer needs to state that a task must be completed according to a referenced standard or instruction rather than personal interpretation. It is shorthand, but the real meaning sits in the document or rule it points back to.
Why it matters
If a team ignores the reference behind IAW, they may execute the task against the wrong standard or document set. That is why this abbreviation has compliance weight far beyond its size.