'Definite bud' is a rather obscure term used to describe buds that are observable - readily apparent to the eye. As close as you can get to the opposite of definite buds are 'latent' buds, sometimes called 'shadow buds', which are not readily observable and are often hidden in bark, bark crevices or under bark scales. The term is most often used when describing pruning practices. E.g., "prune branches back to just above a 'definite bud' facing in the direction you would prefer the branch to grow." This would be a partial description of something we utilize extensively in bonsai, that being 'directional pruning'.

Al