Can you please explain what is meant by "there will be idghaam bil-khulf"

Question
Assalaamu Alaykum

Can you please explain what is meant by "there will be idghaam bil-khulf"

Answer
Wa alaikum assalam wa rahmatullahi wa barakaatuh
When any rule of a particular reciter is stated بالخلف it means that way of recitation has two allowed ways of reciting, the way described, in this case idhghaam, and its opposite, which would mean in this case idh-haar.  So the recitation which has idghaam بالخلف of a particular letter combination or a special word, there are two allowed ways, idghaam and idh-haar.