This is the 3730th most frequent Russian word.
учителей
"Учителей" means "teachers" (genitive or accusative plural in Russian).
Here, 'учителей' is used as the plural genitive case of 'учитель' to show possession.
Я слушаю советы учителей.
I listen to the teachers' advice.
In this example, 'учителей' is the plural genitive case, used after the verb 'не хватает', which requires this case to convey lack or absence.
В школе не хватает учителей.
The school is lacking teachers.
Here, 'учителей' is used again in plural genitive case to indicate that the opinion belongs to the teachers.