Walk alongside is a phrase that means to accompany someone or something while walking. FLANK is a synonym for this phrase, and it is defined as to stand or move at the side of something or someone. This phrase is often used in military terms, where soldiers are instructed to walk alongside one another in order to protect each other from any potential threats. It can also be used in a more general sense, such as when two friends are walking together and want to stay close to each other.