The words seam, seem sound the same but have different meanings and spellings. Why do seam, seem sound the same even though they are completely different words?
The answer is simple: seam, seem are homophones of the English language.
A line of junction formed by sewing together two pieces of material along their margins.
A similar line, ridge, or groove made by fitting, joining, or lapping together two sections along their edges.
To give the impression of being; appear: The child seems healthy, but the doctor is concerned.
To appear to one's own opinion or mind: I can't seem to get the story straight.
To appear to be true, probable, or evident: It seems you object to the plan. It seems like rain. He seems to have worked in sales for several years.
To appear to exist: There seems no reason to postpone it.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.
If they are spelled the same then they are also homographs (and homonyms); if they are spelled differently then they are also heterographs (literally "different writing").