A soft spot is a particularly strong feeling of tenderness for something or someone. It may be more common to have a soft spot for puppies, but it's fine if your soft spot is for stingrays.
A slightly different kind of soft spot is a vulnerability or weakness, especially something that an opponent might take advantage of. And a baby's soft spot has another meaning altogether—it's the vulnerable area on top of her tiny head, where the skull hasn't yet grown together, also known as the fontanelle. This soft spot allows the brain of a baby human to continue growing after birth.