Hello my mum just noticed a pea sized small hard and not moveable lump on the back of her neck just a bit over her hair line it doesn't hurt she is 34?

Lump. This may be an ingrown hair, inclusion cyst or a burnt out old lymph node. It would have to be examined by a physician to be sure. It may need no treatment if there is no inflammation(redness and tenderness) present. If it enlarges or new lumps appear, more concern is raised and more evaluation and testing are needed.