Social engagement is the measurable interaction people have with content: shares, comments, posts, participation. For a physical venue the interesting question is not the metric but how a place prompts it.
Screens do this well when they give people a reason to lift a phone: something worth photographing, a hashtag with a visible payoff, or a moment that only exists in that location. The mechanism is the same one that makes a mural a marketing asset.
The caveat is that engagement is a proxy, and a weak one when it is the target. Likes and shares correlate with attention, not with buying, and a campaign optimised for them reliably produces content that travels among people who will never be customers. It is worth measuring and dangerous to maximise.
The version that survives scrutiny ties the interaction to something identifiable: a code redeemed, an account created, a visit attributed. If the only outcome is a number in a social dashboard, the campaign has not yet been connected to the business.