- surprised or confused by something unexpected
- surprise or shock somebody so much that they do not know how to react for a short while
- startled by some sudden events
- We were all quite taken aback by his decision to retire from upcoming football tournament.
- I was really taken aback by her rude and childish behaviour.
- She was taken aback when he asked her to marry him out of the blue.
- He was taken aback by the direct questions posed by the interviewer.
- The officer was a bit taken aback when I asked him directly whether he was asking for money to do the job.
- The harsh criticism did take me aback a bit, but I recovered enough to blurt out a clarification.
- The woman's angry reaction to his question took him aback.
The phrase comes from sailing. Ships were said to be "taken aback" if the wind was blowing straight into its sails and pushing it backwards. It has been used since the 17th & 18th century. The figurative meaning of the phrase alludes to something that is startling enough to make us jump back in surprise or shock. This version has been in use since the 19th century. An early reference is in The Times in March 1831.
The phrase is generally used in the passive voice (taken aback). The active voice (take aback / take somebody aback), although correct, is used far less.