Dextrose, refined from corn starch into simple glucose, is about as close to pure fermentable sugar as a homebrewer's shelf gets — no malt character, no colour contribution, and essentially complete fermentability, meaning yeast converts nearly all of it to alcohol and CO2 with none of the unfermentable residue a base malt's wort leaves behind.
Its most common homebrew role is priming sugar at bottling time, where a precisely calculated dose produces a target carbonation level — see the priming sugar calculator for how much a specific batch needs at a specific temperature and target carbonation. Used earlier, in the boil itself, dextrose serves a different purpose: raising ABV and thinning body without adding proportional malt character, since 100% of it ferments out rather than contributing to the malt backbone the way base malt extract does. Belgian tripel and other strong, dry-finishing Belgian styles use this technique deliberately, dosing sugar specifically to keep a high-ABV beer from also reading heavy and cloying. Cane (table) sugar functions almost identically for this purpose and is often used interchangeably, though some brewers report subtle flavour differences between the two at higher dosages — dextrose reading slightly more neutral, cane sugar carrying a faint hint of its own origin. Neither contributes meaningful colour or head-retention protein, which is worth remembering before reaching for either as a general-purpose way to boost gravity without a clear reason.