What does these terms mean?
I think these definitions still have a degree of subjectivity and I don't think they are mutually exclusive.

Convergent amplification basically means that "similar" cancers/neoplasms have "similar" amplification patterns, i.e. at around the same loci (see Myllykangas S et al.,2006 for an example).

Focal genome amplification is defined as "CNA [copy number alteration] of limited size, frequently enriched for cancer driver genes" (Krijgsmanthis et al., 2014).