Term deposits, as the name implies, are fixed for a period. If you want to withdraw money prior to the end of the term, there are often penalties.
With an online savings account, the money is at call, so you can get it back whenever you want. As for why you would choose a term deposit over an online savings account if they have the same rate, you wouldn't. High interest online accounts have really supplanted term deposits. Used to be you needed term deposits to get more interest.
Alex
And banks like ING will pay more for a term deposit than their linked Internet account.
From their recent bit of email, the standard rate for the linked account is now 6.4% but they have a 90 day term deposit for 7%, and up to 7.6% for 2 years.