Purpose shapes the design
Training treats and everyday treats are usually designed around different jobs, even when they end up in the same treat jar. Training treats are built for speed and repetition, small, soft, and quick to eat so a dog can get back to the task at hand within a second or two, which matters when you're doing dozens of repetitions in a single session. Everyday treats, by contrast, are often designed to be a longer, more satisfying experience, a bigger biscuit, a chew, or something meant to be enjoyed and lingered over rather than gulped down mid-exercise.
Size and format differences
The clearest practical difference is size: training treats are typically pea-sized or smaller, either naturally or because they're designed to be broken apart easily, while everyday treats are often full-sized biscuits, chews, or larger pieces meant to be given once and enjoyed slowly. Giving a dog a large biscuit-sized treat for every successful "sit" in a training session would add up in calories fast and slow the pace of the session considerably compared with a tiny, soft training treat.
Calorie density and how often each is used
Training treats are generally used far more frequently within a single sitting, sometimes dozens of times in twenty minutes, so they tend to be formulated to be lower in calories per piece, precisely because the volume adds up quickly. Everyday treats are usually given once or a few times a day, so a slightly higher calorie count per piece is less likely to throw off the daily balance, provided the overall treat guideline is still respected.
Can you use one for the other?
There's no strict rule against it, many owners simply break a larger everyday treat into small pieces to use for training, and it's a perfectly reasonable way to stretch a treat and control portions more precisely. The main downside is convenience: pre-sized training treats save time and mess compared with breaking apart a bigger treat mid-session, which matters when you're trying to keep training sessions fast-paced and your dog's attention high.
Choosing based on the context, not the label
Rather than treating "training treat" and "everyday treat" as strict categories, it's more useful to think about what the moment actually calls for, fast, low-calorie, and easy to eat for training repetitions; more substantial and satisfying for a one-off reward or a relaxed evening chew. If you're ever unsure whether a specific treat is appropriate for frequent use given your dog's size, weight goals, or health conditions, your vet can help you match the right format to your dog's actual needs. Keeping both a training-sized option and a larger everyday option on hand covers most situations without needing a whole cupboard of different products.