担保 (dān bǎo) means 'to guarantee, to vouch for' and is used in formal, often legal or financial contexts — e.g., a person or institution backing a loan. It is more specific than 保证 (bǎo zhèng), which is a general promise or assurance used in everyday speech. 确保 (què bǎo) focuses on 'ensuring' a result, while 保障 (bǎo zhàng) emphasizes 'safeguarding' rights or security.