The Great Tit (Parus major) is the largest of the Tit (Parus) family with the male being more bright yellow, slightly larger and more robust than the female.
The most distinctive feature is the black stripe from the throat down the rest of the body (like a neck tie).
Males can be distinquished from females by having a broad black stripe that widens between their legs.
The black stripe on females is much shorter and narrower.
More dominant males have a broader black stripe than other males and are considered more attractive to females.

1st, 2nd & 3rd photo: A male. Combloux, Haute-Savoie, France, 17 March 2018
4th photo: A female. Combloux, Haute-Savoie, France, 10 March 2017