You can understand the concept of Letter of Weakness with the help of following points.

(i) The auditor does compliance procedure to ascertain that the internal control system exist in the entity; it works effectively; it work continuously in the entity during review period.

(ii) When he comes across any weakness in the control points, he issues letter of weakness.

(iii) Letter of weakness is a report issued by auditor stating the weakness in internal control mechanism. It also suggests measures by which the weakness in the system be corrected and the control system be made better protected.

(iv) Lapses in operation of internal control too are reported in the communication of weakness.

(v) The communication of weakness is reporting to management of such weakness in design and operation of internal control as have come to notice of auditor during his auditing and it should not be taken to be a review and comment on adequacy of the control mechanism for management purpose.