Staying on topic is very important in debates and discussions. A Red Herring is a statement or question that distracts from the subject at hand. This often happens in a number of ways:

• One person realizes they are losing the debate and purposefully changes the subject to something they feel more comfortable debating.
• The topic reminds someone of a related but off-topic idea. This is is brought up, changing the subject, often without realizing it.
• Someone bring up relevant but tangential supporting point with the intention of bring it back the original point but they never return do.

A Red Herring can seem similar to a Strawman, the distinction being a Red Herring changes the topic while a Strawman changes the opponent's argument.