How do you define ‘traction’?

Users? Revenue? CPA? Press? Traffic? This view is (hopefully!) from an investor’s perspective, and treats ‘traction’ as different from internal management metrics. What is it? I’ve always liked Naval Ravikant‘s basic definition: ‘Quantitative evidence of market demand.’ Traction is proof that somebody wants your product. Ideally, it should communicate momentum in market adoption. What works?…