Broadly speaking, a witness in a court proceeding is only supposed to testify as to what he or she observed, and is not to give an opinion on what specifically was observed. However, there are two exceptions to this general rule. Expert evidence, and non-expert evidence given by a layperson. Generally, lay opinion evidence refers to evidence given by a witness who is not an expert witness, but who testifies as to opinions and/or inferences.
In American Creek Resources Ltd. v. Teuton Resources Corp., the Supreme Court of British Columbia summarized the breadth of lay opinion evidence.
 Generally, opinion evidence is inadmissible unless it is expert evidence. There are exceptions. Lay opinion evidence may be admissible under circumstances discussed at length in Part II of Chapter 12 in The Law of Evidence in Canada, where the learned authors state at paragraph 12.14:
Courts now have greater freedom to receive lay witnesses’ opinions if: (1) the witness has personal knowledge of observed facts; (2) the witness is in a better position than the trier of fact to draw the inference; (3) the witness has the necessary experiential capacity to draw the inference, that is, form the opinion; and (4) the opinion is a compendious mode of speaking and the witness could not as accurately, adequately and with a reasonable facility describe the facts she or he is testifying about. But as such evidence approaches the central issues that the courts must decide, one can still expect an insistence that the witnesses stick to the primary facts and refrain from giving their inferences. It is always a matter of degree. As the testimony shades towards a legal conclusion, resistance to admissibility develops.