Strange patch

I have noticed this strange patch appear on my Hallway way at bottom of the stairs next to my downstairs cupboard.
Its never been there before and its does not feel damp or have any form of mould near or around it.
I have tried drying it out but it does not seem to go, but has got bigger.
There is no water pipes or anything near the area.
Any help would be fantastic.

Many Thanks

Looks like damp to me, treat yourself to a damp tester from somewhere like Screwfix, toolstation or amazon lots around starting from around a tenner up to silly money!

Don't need to spend a fortune, something like this will be fine for your needs.
https://www.toolstation.com/draper-mini-moisture-meter/p55818