Planetesimals are a class of small solid objects that are supposed to have coalesced into protoplanet/dwarf planets. They orbit a star and form through shared gravitational attraction. Should they accumulate more mass, they could graduate into full planetary status.
Note: The word “planet” along with everything below and above that status comes solely based on International Astronomical Union (IAU) definitions of the terms, where as ancient Greeks dubbed anything moving across a veil of fixed stars as wondering stars (planetes asteres, where asters=stars).