Webyeshiva.org has a series of classes from Corey Beinhaker about reading the megilla (you have to log in to access the files, but registration is free). In the first class, about 29 minutes in, he brings a quote from a footnote in the "Piskei Teshuvot" (I'm not sure which sefer that is). That says that according to the Siddur Yaavitz and the Elyah Rabba (690:19), it means to raise your voice and continue the tune uninterrupted.
Mr Beinhaker explains that "the voice is raised and the pace is picked up and held at a constant level, both in terms of voice and pace"
He gives some examples.
These verses seem to fall into two categories. The first is "Piskei Ge'ula", verses of redemption. The second are verses or parts that hint to G-d's name.