PMI stands for private mortgage insurance and is charged to homeowners when less than 20% down payment is used. PMI "drops off" when the homeowner has a loan-to-value ratio (LTV) of 80% or less. LTV as it relates to automatic PMI removal is calculated based on the purchase price, not the current market value.
If you performed a renovation that increased the value of your house, or the value of houses in your neighborhood has increased to a point where you believe you have an LTV of 80% or less based on current market value, then you can contact your mortgage servicer and request PMI removal.
Many people buy houses with a low percent down payment (i.e. 5% down), conduct a cost-effective rehab and then request PMI removal. Successfully removing PMI can reduce your monthly PITI expense considerably.