A foundation or base; the underlying support or basis for something (physical or abstract).
家を建てる前にしっかりと土台を作る必要がある。
Before building a house, you need to make a solid foundation.
語学学習の土台は毎日の復習だ。
The foundation of language learning is daily review.
彼の説明は論理の土台が弱く説得力に欠ける。
His explanation lacks a strong logical basis and is unconvincing.
From the beginning; inherently or by nature — often used in negative contexts (e.g. '土台無理だ' meaning 'it's impossible from the start').
その計画は土台無理だから、見直すべきだ。
That plan is impossible from the outset, so it should be reconsidered.
彼に頼んでも土台当てにならないよ。
Even if you ask him, he won't be reliable from the start.
土台あり得ない話だ。
That's a story that's impossible from the outset.