sociala

Two adjectives, and the difference is real. Esperanto has both socia and sociala, and PIV keeps them apart:

• socia is of society, societal. Socia klaso, sociaj problemoj, socia vivo.
• sociala is of social provision - welfare, benefits, the machinery a state runs to look after people. Sociala asekuro is social insurance, socialaj servoj are social services, sociala helpo is welfare payment.

Socia is the native build: socio plus the adjective ending -a, and nothing more. Sociala is a whole borrowed adjective. This matters because of the letters in the middle: -al- is not an Esperanto suffix. Ido adopted one; Esperanto never did. So sociala cannot be parsed as soci- plus -al- plus -a - the root is social-, borrowed entire from French, and the resemblance to a suffix is the false seam.

Teach both sides, because the community argues about it. A good many careful writers regard sociala as an unnecessary Gallicism and use socia for both jobs; others keep the split because socia asekuro really is ambiguous. The safe rule for a learner: write socia unless you specifically mean welfare provision, and you will never be wrong. The one place the l is fixed and nobody quarrels is socialismo and socialisto - nobody writes sociismo.