Kerning is the adjustment of space between individual pairs of letters in a wordmark or lettermark, fine-tuned beyond a font's automatic default spacing to make the overall word read smoothly and evenly.
Certain letter combinations (like "AV" or "To") naturally create uneven visual gaps if left at default spacing — professional kerning corrects these so the word reads as one balanced unit rather than a collection of individually spaced letters.
Poor or default kerning is one of the most common tells of an amateur or DIY logo — it's a small detail, but a trained eye (and often an untrained one too) notices it immediately.