In ArcMap software, data is displayed on a map using a specified coordinate system. When additional data is added to the map does that not use the same coordinate system, ArcMap can project this data ‘on the fly.’ That is, ArcMap can automatically transform the data’s projection system to be the same as that used for the map. In ice hockey, the majority of line changes occur ‘on the fly’, that is, while play is still ongoing. Players leap over the boards as quickly as possible as their line is substituted in to avoid any prolonged shifts and to ensure that fresh players remain on the ice as often as possible. It can mean to make a copy of a removable media (CD-ROM, DVD, etc) directly, without first saving the source on an intermediate medium (a harddisk), for example, copying a CD-ROM from a CD-ROM drive to a CD-Writer drive. When used for encrypted data storage, on the fly the data stream is automatically encrypted as it is written and decrypted when read back again, transparently to software. The acronym OTFE is typically used. Source.