Hierba vs. pasto vs. césped vs. grama
The Spanish language has various words to denote 'grass', such as 'hierba', 'pasto', 'césped', and 'grama'. Although they all refer to different types of grass, there are subtle differences in their use and meaning which can vary by region.
Hierba
This is a generic term for any type of plant that does not have a wooden stem, including grass. It is widely used throughout the Spanish-speaking world.
Las ovejas están comiendo hierba en el campo.
(The sheep are eating grass in the field.)
Pasto
Also a general term for grass that's usually eaten by livestock. It can also broadly refer to grazing land. This term is frequently used in Latin America.
El ganado necesitaba más pasto para alimentarse.
(The cattle needed more pasture for feeding.)
Césped
'Césped' specifically refers to manicured or cultivated grass, like that found in gardens, lawns, sports fields etc. This word is commonly used in Spain.
El césped del campo de fútbol está muy verde y bien cuidado.
(The grass on the soccer field is very green and well-maintained.)
Grama
'Grama' refers to a certain type of low-growing grass that spreads by stolons (lateral growing stems). It's often used to create dense, carpet-like lawns or turf.
Nuestro jardín está lleno de grama verde y fresca.
(Our garden is filled with fresh and green Bermuda grass.)
Summary
'Hierba' is a general term for plants including grass, 'pasto' refers broadly to pasture for grazing or the grass itself, which is commonly eaten by livestock, 'césped' denotes manicured or cultivated grass areas and 'grama' relates specifically to a type of durable, spreading lawn grass. The words may be used somewhat interchangeably, but these nuances can help provide more specificity.