Brand architecture is the structure a company uses to organize multiple brands, sub-brands or product lines, and how clearly (or not) each one is connected to the parent brand.
Common structures range from a "branded house" (one master brand covering everything, like a single company name across all products) to a "house of brands" (distinct, separately branded products with little visible connection to the parent company).
Most small and mid-size businesses don't need complex architecture, but it becomes a real decision once a business launches a second distinct product line, service tier, or sub-brand and has to decide how closely to tie it to the original identity.