Thank you for your question. The Infallibles is a translation of the word Maʿṣūmīn in Arabic, which means those people that are protected from committing sins. They are protected because of the knowledge they have concerning the different sins and their outcomes. They are also protected from performing what is second best, meaning they always make the best choices because of their wisdom. These are very high stations that are only possible by Allah, His Wisdom and His Will and has been vastly theorised in Shii theology, philosophy and mysticism. However, the basis of this understanding of the infallibity of the Ahl al-Bayt (as) is the scriptural sources.
May you always be successful