It means back to what you usually do, i.e. work, school, etc.
It comes from the term "grind stone", but has since built up its own meaning.
"Back to the grind" is a colloquial phrase used to describe returning to work or regular daily tasks after taking a break or vacation. It suggests a transition from leisure or relaxation back to routine responsibilities.
back to work
Back to the Grind - 2007 was released on: USA: 18 July 2007
Youngin' on his grind refers to a young man doing his routine work. Youngin' meaning a young person; grind as in, "Back to the old grind".
back to the grind
Back to the Grind - 2007 - TV Series - Reality SUSPENDED was released on: USA:2007
john key is the vice president
Harder Than It Looks - 2012 Back to the Grind 1-3 was released on: USA: 12 September 2012
Molars are the teeth found at the back of the mouth. Their purpose is to grind food.
Back to the Grind - 2007 Loni Anderson and Erik Estrada 1-1 was released on: USA: 18 July 2007
Grind
if we lose our teeth we cannot crush and grind our food
Molars, the teeth in the back of your mouth.