This is the 11725th most frequent Russian word.
завтрака
"Завтрака" is the genitive singular or accusative plural form of "завтрак," which means "breakfast."
Here, 'завтракаю' is the first-person present tense verb meaning 'I have breakfast', denoting the speaker's habitual action.
Завтракаю каждый день в восемь утра.
I have breakfast every day at eight in the morning.
'Завтрака' here functions as the genitive case form of 'завтрак' (breakfast), part of the prepositional phrase 'после завтрака' which means 'after breakfast'.
После завтрака я пошел на пробежку.
After breakfast, I went jogging.
In this sentence, 'завтрак' acts as a noun in its nominative case 'завтрак,' signifying the meal (breakfast) directly.