A right to buy shares at a fixed price before a fixed date, usually handed out as a sweetener alongside a placement.
A security that gives the holder the right to purchase shares at a specified price (strike price) within a certain time period. Warrants are often issued as part of private placement financings in junior mining companies.
Warrants are future dilution at a price you already know. Enough of them clustered near the current share price will cap a stock for years, because every rally into that strike releases new supply.
Find the strike prices and expiry dates in the financing releases, then compare them to where the stock trades. Warrants deep in the money are effectively shares already; warrants far out of the money and near expiry are usually irrelevant.
Reading share count alone. A company with modest shares outstanding and a large warrant overhang is more diluted than it looks.