salam, please can you explain what Al-lahm is and give some examples?

Question
salam, please can you explain what Al-lahm is and give some examples. jzk

Answer
Wa alaikum assalaam wa rahmatullahi wa barakatuh,
Most likely you mean , with a as the last letter.  The word linguistically means a mistake.  In applied tajweed, it means a mistake and deviation from correctness when reading. 
is divided into two categories in tajweed:
1. is an obvious and clear mistake. It is a mistake that occurs in the pronunciation of the that affects the accuracy of the reading.  An example of this would be reading the letter  as a .

2. is an obscured and hidden mistake. It is a mistake that enters the reading but is only heard and known by an accomplished reader. It is not a mistake that leads to a change in the meaning, or language, or grammar.
An example of this would be to not hide a saakinah when followed by one of the letters of ikhfa', or not lengthen the four vowel counts.