This is the 3278th most frequent Russian word.
основная
"Основная" means "main" or "primary" in English.
In this sentence, 'основная' acts as an adjective, meaning 'primary' or 'main,' used to describe the task as the most important one.
Основная задача данного проекта заключается в улучшении экологии.
The primary goal of this project is to improve the environment.
Here, 'основная' describes 'idea,' signifying it as the core or fundamental concept.
Её основная идея состояла в создании нового подхода к обучению.
Her main idea was to create a new approach to teaching.
In this case, 'основная' qualifies 'part,' indicating it as the major or central component.