Definition
Brand normalization is resolving the different ways a brand is written in answers to a single entity: casing, punctuation, legal suffixes, a product line named instead of the company. Without it the same brand appears as several rows in a share-of-voice table.
Why it matters
Splitting a competitor into two rows understates it and flatters you; splitting your own brand understates you. Both are silent, and both make the ranking wrong rather than merely imprecise.
How to measure it
Reduce each name to a comparison key before counting, and review the tail of the brand list for near-duplicates after every run. Product lines that belong to you should be mapped to the parent brand deliberately, not left to chance.