In US equities the two familiar items are the SEC Section 31 fee, charged on the notional value of sales, and the FINRA trading activity fee, charged per share sold. Rates are adjusted periodically, so any figure you memorise will drift.
They are small but asymmetric: only the sell side pays, which makes them a fixed cost of every exit regardless of whether the trade worked.
Example: at an illustrative rate near $27.80 per million dollars of sales, selling $50,000 of stock costs about $1.39 in Section 31 fees, plus a per-share activity fee of roughly $0.000166 with a per-trade cap. For a trader turning over $2 million of sales a month, that is about $56 — trivial alone, but part of a stack that adds up.
Related: commission, exchange-fee, finra, sec