Funds transfer between spouses accounts

Helllow experts,

As the title suggests, my query is whether fund transferred between spouses acccounts are in nature of loan or gift or what else? What are the income tax implications of such transfers? It may be worth noted here that husband or wife transferring fund to each others accounts for any reason is very common thing (may it be in small amount or big) and usually such funds are not repaid because they are considered to be family affair between the two (in a common paralance that - how there can be loan transaction between husband and wife which is very much right also). What should be the accounting treatments to such transactions, whether loan or something else?
Please explain in detail with relevant references.

Thanks in advance.