You’re definitely not alone.
Many use the terms interchangeably.
So, here’s what you need to know about purebred dogs, mixed breed dogs, and hybrid dogs…
Once a dog is registered with the American Kennel Club (AKC) or the United Kennel Club (UKC), the dog’s owner receives a pedigree (family tree, lineage showing the dog’s ancestors are all from the same breed) along with the dog’s own registration papers.
When the lineage of a purebred dog is recorded, that dog is said to be pedigreed.
Purebred dogs were developed by "selective breeding", which means dogs with specific traits (carried on genes inside the dog’s body) were bred, whereas dogs with different traits (and thus differing genes) were not bred (i.e. their traits and genes were removed from the gene pool). The result is that every breed ends up with a specific set of genes that distinguishes it from every other breed. These genes include physical traits such as size, coat, and color. Source
Mixed Breed Dogs
A mixed breed dog is the offspring of 2 or more different dog breeds where neither the mother nor the father is a registered purebreed dog. Usually the mixed breed dog’s ancestry is unknown.
Mixed breed dogs are commonly referred to as mutts — which, by the way, is not a derogatory term.
Quite often, owners of mixed breed dogs affectionately and proudly refer to their dogs as mutts — because they are loved for who they are, not for their specific genetic makeup or their papers.
In the simplest terms, a hybrid dog is the offspring of 2 or more known, but different, dog breeds.
Technically, a mixed breed dog is not a hybrid — because a hybrid dog is the offspring of 2 different species (not just the offspring of 2 different breeds). However, people have been calling mixed breed dogs hybrids for some time now.
The American Canine Hybrid Club recognizes a hybrid dog as the offspring of 2 purebreed dogs. The mother and the father must both be registered as a purebreed dog.
That means if a dog that has a purebreed for one parent, but a mixed breed for the other parent, it is not a hybrid dog, per se. It’s simply a combination of breeds, or a mixed breed dog.
For what it’s worth, hybrid dogs of 2 purebreed parents are often called designer dogs.
The Encyclopedia Britannica traces the term "designer dog" to the late 20th century, when breeders began to cross purebred poodles with other purebred breeds in order to obtain a dog with the poodles’ hypoallergenic coat, along with various desirable characteristics from other breeds. One connotation of the term "designer dog" is that the breeding is by design, between a deliberately chosen sire and dam, as opposed to an accidental breeding. A few breeders have taken this a step further, breeding a specific crossbreed to others of the same cross, setting a standard, and documenting the ancestry of puppies so bred over generations, in order to create a new breed of dog. Source