This is a Belarusian SSR (BSSR) commemorative pin connected to the VDNH BSSR, which was the Belarusian branch of the Soviet Exhibition of National Economic Achievements (ВДНХ — the big USSR-wide expo of science, agriculture, and industry).
What the pin says
ВДНХ БССР — “VDNH BSSR” (Exhibition of National Economic Achievements of the Byelorussian SSR)
60 — Likely marking the 60th anniversary of something
КАСТРЫЧНІК — This is Belarusian for “October”, referring to the October Revolution (Кастрычніцкая Рэвалюцыя)
Meaning
This pin was produced to commemorate the 60th anniversary of the October Revolution, celebrated in 1977 across the USSR. Belarus produced its own themed pins, often featuring national costumes, the BSSR flag (visible at the top), and symbols of agriculture or culture.
So this is a 1977 VDNH BSSR 60th Anniversary October Revolution souvenir pin.