Assalamu Alaikkum wa rahmatullahi wa barakatuhu,
Kalimah literally translates into word in arabic or speech (I've heard scholars use this word for speech). But, in the above context, I think he means Kalimah of Tawheed or Shahada. i.e. La Ilaaha ill-Allah .
It is statement that differentiates between kufr and Islam and it is the statemen of taqwa as was made by Ibrahim (Alayhi salam )
Surat Az-Zukhruf [43:28]
And he made it a word [i.e.La Ilaaha ill-Allah] remaining among his descendants that they might return [to it].
But, it is not the mere utterance of it that will keep us of hellfire, but one should understand it, recognize it in heart and love it and its people and have hatred towards anything that opposes it.
This statment has a negation and affirmation as explained by Shaykh Muhammad ibn Abdul Wahhab i.e. negation of worship to anyone except Allah and affirmation that worship belongs only to Allah. That we seek aid of no one but Allah and that Uloohiyah (servitude) is only to Allah. So there is no intermediaries between a person and Allah.
