Learn Italian: Lo verifico prima che il termine scada. - I verify it before the deadline expires.

Because the phrase prima che (before) introduces an action that hasn't happened yet, so it always requires the subjunctive mood. scada is the third-person singular present subjunctive of scadere (to expire).

Can I use prima di instead of prima che in this sentence?

Not here. You use prima di plus the infinitive when the subject of both actions is the exact same. Here, the subjects are different: 'I' verify it, but 'the deadline' expires. Because the subject changes, you must use prima che plus the subjunctive.

Is termine the normal word for 'deadline'?

It depends on the context. termine can mean 'word', 'term', or 'end', but in business, academic, or administrative contexts, il termine is the most common way to say 'the deadline' or 'the time limit'.

Why is lo at the very beginning of the sentence?

lo translates to 'it' and is a direct object pronoun. In Italian, these pronouns must be placed immediately before the conjugated verb they belong to, which is why it sits right before verifico.