The common word for "dad" in Mandarin is 爸爸 (bàba). It's informal and affectionate, used by children and adults alike when speaking to or about their father — similar in tone to "dad" or "daddy" in English, not as formal as "father."

Some related terms:

• 爸 (bà) — can be used alone, especially in the phrase 我爸 (wǒ bà, "my dad") when talking about him to someone else.
• 父亲 (fùqīn) — the formal, written word for "father," used in essays, official contexts, or when speaking more seriously/respectfully.
• 老爸 (lǎobà) — a casual, slightly joking way to say "dad," popular among younger speakers.

Example: 我爸爸是老师。(Wǒ bàba shì lǎoshī.) — "My dad is a teacher."

Note the tone pattern: 爸爸 is pronounced with the first syllable in full fourth tone (bà) and the second syllable often neutral or lightly toned in casual speech, though textbooks usually write both as fourth tone (bàba).