BIS - Blackberry Internet Service
BES - Blackberry Enterprise Server
OWA - Outlook Web Access
Now that you know what that acronyms are for, here's a little info on what each one is.
BIS - This is the service that allows individuals to forward e-mail to their Blackberries. This can be their work e-mail (assuming it's approved of course), personal e-mail such as yahoo or gmail, or business e-mail (firstname.lastname@example.org, etc). I believe as long as the e-mail server that holds your e-mail supports POP3/IMAP, SMTP, or OWA, you can receive your e-mail on your phone. I believe there's even a client redirector that can redirect e-mail to your phone if your e-mail server isn't supported though I'm not certain on this one.
BES - Is primarily for companies that want to let their employees have remote access to e-mail for productivity type purposes (sales people, executives, etc) or job reasons (IT people, etc) but want to maintain control over what's allowed on the phone.
OWA - Is used in conjunction with a Microsoft Exchange server and is the web interface to Exchange. It can be used for Blackberry purposes as well as "push" e-mail with Windows mobile devices or can just simply be a web interface to your e-mail.