The severance is your notice.

We will lay you off in 3 months - and having for a 3 months dead man walking in the company is probably worse for everyone. Since said employee probably won't break records for productivity during this period - it is easier for everyone just to give the one let go some lump sum.

Anyway I think that in this post the context is that they will be let go during good times - without the informal - we know the company is in trouble and layoffs as coming common knowledge that big companies have.