1. To copy data (often program code to be run) into memory, possibly parsing it somehow in the process. E.g. "WordPerfect can't load this RTF file - are you sure it didn't get corrupted in the download?" Opposite of save.
2. The degree to which a computer, network, or other resource is used, sometimes expressed as a percentage of the maximum available. E.g. "What kind of CPU load does that program give?", "The network's constantly running at 100% load". Sometimes used, by extension, to mean "to increase the level of use of a resource". E.g. "Loading a spreadsheet really loads the CPU". See also: load balancing.
3. To install a piece of software onto a system. E.g. "The computer guy is gonna come load Excel on my laptop for me". This usage is widely considered to be incorrect.