A more thorough explanation:

The contemporaneous-objection rule is a legal doctrine that requires a timely and proper objection to be made during a trial for the issue of admissibility to be considered on appeal. This means that if a party wants to challenge the admissibility of evidence presented during a trial, they must object to it at the time it is presented.

An objection is considered timely if it is made as soon as possible after the evidence is presented. It is also considered proper if it is made formally on the record. These requirements give the trial court a chance to correct any errors and preserve the issue for appeal.

For example, if a lawyer believes that a piece of evidence is irrelevant or unfairly prejudicial, they must object to it when it is presented in court. If they fail to do so, they may not be able to challenge its admissibility on appeal.

Another example is if a witness is asked a question that is objectionable, such as one that calls for hearsay evidence. The lawyer must object to the question at the time it is asked in order to preserve the issue for appeal.