In practise, it means it's a dreadnought (large, powerful warship) that incorporates features of science vessels, like improved sensors, and a science-based special weapon."Science Dreadnought".I love these class designation word salads. This one tickles me in particular.
By default, in STO dreadnoughts are dreadnought cruisers, i.e. engineering-division ships. Tactical dreadnoughts are called juggernaut.
Eaglemoss identified the Merian class as science vessel, so at least that gels.