Herbe vs. pelouse vs. gazon

The French words 'herbe', 'pelouse' and 'gazon' all refer to 'grass' in English, but are used in different contexts to refer to specific types of grass or grass-related areas.

Herbe

'Herbe' generally refers to grass or herbs in a broader sense, including various kinds of non-woody plants.
La vache mange de l'herbe dans le champ.
(The cow eats grass in the field.)
J'aime sentir l'odeur de l'herbe après la pluie.
(I love to smell the scent of grass after the rain.)

Pelouse

'Pelouse' specifically refers to a lawn or a mowed area of grass, typically found in gardens, parks, or sports fields.
Les enfants jouent sur la pelouse devant la maison.
(The children play on the lawn in front of the house.)
Il est interdit de marcher sur la pelouse du parc.
(It is forbidden to walk on the park's lawn.)

Gazon

'Gazon' can refer to turf or sod, and it is often used in contexts related to gardening, landscaping, or when referring to the material itself rather than an area.
Nous allons poser du gazon dans notre jardin ce weekend.
(We are going to lay sod in our garden this weekend.)
Le gazon synthétique peut être une bonne alternative pour les terrains de sport.
(Synthetic turf can be a good alternative for sports fields.)

Summary

While 'herbe', 'pelouse' and 'gazon' can all be translated as 'grass', 'herbe' generally refers to grass or herbs, 'pelouse' refers to a mowed lawn, and 'gazon' is used for turf or sod, especially in gardening contexts.