Full explanation
ARR is your Annual Recurring Revenue. It is how much money your subscriptions would generate over one year if nothing changed.
Investors love ARR because it gives a clear yearly picture of the business size. Once you reach 100 000€ ARR or 1 000 000€ ARR, you have hit milestones the market understands.
You compute it by taking your MRR at the end of a month and multiplying by twelve.
Concrete example
Your MRR is 5 000€ this month. Your ARR is 60 000€. If you grow your MRR to 8 000€, your ARR becomes 96 000€.