What's a Scenario

In general, "scenario" usually means a possible sequence of events.

In the software industry, "scenario" usually means one of the following:
1. Same as a use case
2. Path through a use case
3. Instance of a use case

#3 is generally preferred because it provides a testable instance with specific results.

Around Microsoft, we use "scenarios" quite a bit ...
1.  At customer events, it's common to ask, "What's your scenario".  This is another way of asking, "what's your context?" and "what are you trying to accomplish?"
2.  In specs, scenarios up front set the context for the feature descriptions.
3.  Marketing teams often use scenarios to encapsulate and communicate key customer pain/problems.
4.  Testing teams often use scenarios for test cases.

At the end of the day, what I think is important about scenarios is they help keep things grounded, tangible and human.  I like them because they can stretch to fit, from fine-grained activities to large-scale, end-to-end outcomes.