Monthly Recurring Revenue, commonly abbreviated as "MRR" is all of your recurring revenue normalized into a monthly amount. It's a metric usually used among subscription and SaaS companies.
MRR looks at all of your various pricing plans and billing periods and consolidates them into a single number that you can track the trend of over the life of your business.
While MRR is a highly valuable metric, it is not an accounting metric and shouldn't be used for that. When you have a mix of billing intervals (weekly, monthly, quarterly, annual) they all get normalized into a single "monthly" figure and so the figure can be misleading when it comes to how much money you're actually bringing in.
We find that the trend is more important than the number itself.