Proposition 2 1/2 limits the annual increase in total property taxes to 2.5%, plus additional taxes assessed on new construction or major additions. However, if the assessed value of your property increased faster than the average of all properties in town, your property taxes may have increased more than 2.5%, while the tax on properties that increased in value more slowly may have increased less than 2.5%.
Deputy Town Manager Sandy Pooler has written an excellent explanation of this, which you can read here.