Can someone define what the IRS means by "Similar Items"?

I've donated well over $10,000 in non-cash charitable donations while clearing out a family member's estate this past year.  I am confused by the IRS definition of similar items.  In my mind, clothing, furniture, books, small appliances, computer equipment, electronics so on and so forth would NOT be similar items.  Some people are advising me all those items are considered household items therefore they would be considered similar items.  Which is it?