Q:

What does it really mean that a Moslem women accused of Zina or adultery needs to provide four witnesses from tg community that vouch for her piety?

A:

In the Name of Allah, the All-Merciful, the Mercy-Giving.

All praise is due to Allah. Peace and blessings be upon Prophet Muhammad.

A woman accused of adultery/fornication is innocent until the accusation is proved by four eyewitnesses to the very act of sexual intercourse. Otherwise, the accuser is punishable by eighty lashes. A clear Quranic injunction dictates “As to those who accuse chaste women [of illicit sexual intercourse] who then do not produce four eyewitnesses [to the very act], whip them eighty lashes and do not accept  any testimony from them ever after, for it is these who are the ungodly.” An-Nur 24:4)

However, if it is the husband who accuses his wife of adultery and has no eyewitnesses, then both the husband and his wife have to engage in a process called li`an (mutual invocation of curse) as detailed in the Quranic verses that read “As to those who accuse their wives [of adultery] while having no eyewitnesses but themselves, then the due testimony of each [accuser]  is to bear witness four times, [swearing] by Allah, that he is, indeed, of the truthful- while the fifth [testimony] shall be that the curse of Allah be upon him if he is of the liars. Yet punishment shall be averted from her  if she bears witness four times, [swearing] by Allah, that he is, indeed, of the liars- while the fifth [testimony] shall be that the wrath of Allah be upon her if he is of the truthful.” (An-Nur 24:6-9)

Allah knows best.