Yes! Sometimes it's considered a kind of connective tissue (along with things like bone, cartilage, collagen) and sometimes it's sort of put on its own. But it's definitely a tissue.

a tissue is a group of cells that act as a coherent system in the body, no?

blood is a tissue

blood is a tissue

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Blood is a considered as a tissue.
Cells that build up is a tissue right?
But tissue together is an organ right?

But take note primarily cells together is a tissue.