What is the meaning of truthfulness linguistically and Islamically?

Linguistically, truthfulness (صدق) is the conformity of a judgment to reality. It is also defined as reporting in accordance with what is in reality. The Prophet, peace and blessings be upon him, urged truthfulness, explaining that it leads to righteousness (birr), and that righteousness leads to Paradise. He also stated that whoever is truthful and strives for truthfulness will be recorded by Allah as a siddiq (a truthful one). Truthfulness is in speech and action, and striving for truthfulness (taharrī al-ṣidq) means to exert great effort and diligence in it.