What you can lose on one trade
Risk per trade is the amount of account equity you are willing to lose if your stop-loss is hit. Expressed in currency (e.g. $50) or percent (e.g. 1% of $5,000 = $50).
Professional retail guidelines often cite 0.5%–2% per trade — never risking so much that a few losses destroy the account.
Define risk before entry. If you cannot place a logical stop, skip the trade.