Original: In British English very large venues suitable for major trade shows are known as exhibition centres while the term "convention centre" is sometimes used for intermediate venues between exhibitions centres and "conference centres", which are much smaller and contain lecture halls and meeting rooms.
Simplified: In British English very large venues suitable for major trade shows are known as exhibition centres. The term "convention centre" is sometimes used for intermediate venues between exhibitions centres and "conference centres", which are much smaller and contain lecture halls and meeting rooms.