Keywords to look up, one per entry, e.g. ["bitcoin", "ethereum"] — up to 300 per run. A failed, blocked or empty fetch is never charged; it is named in the run's ERRORS record. Leave this empty and set "Category ID" instead and the run explores that whole category rather than a keyword. Send more than 300 and the run still starts: it uses the first 300 and writes one uncharged row saying what you asked for and what bound it, so run the rest separately. Each term is fetched independently unless Compare is on. Pricing: you are billed at most one trend report per term — one keyword's full timeline, its complete related-queries set and its region table settle together as ONE report, however many of those three you ask for, so all three cost the same as one. Related topics is a separate event, billed on its own. Omit the field entirely (an API call with no input) and the run takes a real, small sample instead — one example keyword ("bitcoin") on the three default surfaces, worldwide, over the last 12 months, inside a three-minute window, charged like any run at one trend report. Change a setting but still leave this empty and you get that SAME live sample, run under what you set — your location, time range, category, search property and choice of surfaces — with one uncharged note naming the settings it ran under. The one thing it cannot do is compare, which needs 2-5 of your own terms: that asks you for search terms on an uncharged row instead.