Cost Basis
Cost basis is the total you paid for a position, fees included; PnL is measured against it.
Quick answer
Cost basis is the total you paid for a position, fees included; PnL is measured against it.
What it means
Cost basis is what you actually paid to acquire a position, including fees. With multiple buys it becomes a weighted average across all of them.
Why it matters
Your cost basis is the reference point every PnL number is measured against, so getting it right matters.
Examples
Buy 1,000 tokens at $0.02 and 1,000 more at $0.04. Your average cost basis is $0.03 per token.