Not sure where I read it, but I think here in the UK, a "sexless marriage" is considered that, where it happens less than once a month. About 10 years of my now annulled marriage, I realise now, could be considered sexless. Very early, she drew a line down the bed and said "this side is mine, this side is yours, dont think of crossing it!".
As she was less experienced than me, I thought it was a sign to let things go at her pace. So I never asked for, or suggested sex, or made any moves. So it was once a month, or even less for 10 years.