While it is true that sperm agglutination and sperm aggregation may seem to be the same thing, there are differences between the two concepts.
Sperm agglutination refers only to the union of motile spermatozoa with each other. It is suggestive of the presence of anti-sperm antibodies.
Aggregation refers to the union of immotile spermatozoa with each other, or of motile spermatozoa with mucus, other cells or cellular debris. It is more nonspecific in nature and is therefore of less clinical relevance than agglutination of motile spermatozoa.