A visual identity helps your trademark or company be recognised at first glance. It reflects your company and should therefore represent its values, while differentiating it from competition. Its style will impact all your in-house and/or external communication.
A visual identity consists in setting up a logo based on which all other communication media will be designed. This forms a graphical line whose criteria are clearly defined in a charter, in order to enhance a unity and visual consistency between the various media.