Once when I was real young I had a rather heated argument with my brother. We argued over if the coat of arms was on Poland’s flag. Little did we understand that many countries have at least two flags, civil and state.
State flags are flags that are reserved for use by the government. Most of the time state flags feature the coat of arms. Civil flags are for general, public, use and most lack the coat of arms. The reason for having a separate civil flag dates back to the past when European sea trade was becoming huge. Both states and merchants wished to identify themselves yet show they were not a military or government entity. This allowed for an operating environment to be created with little confusion on whether the upcoming vessel was hostile or a mere trade competitor.
Today there is less distinction between state and civil flags. Part of the reason is cost. In the past cloth flags with the added complex coat of arms cost more money. This limited use to primarily the government. Today, nylon flags are much cheaper and coat of arms can be printed onto the fabric. Most civil and state flags are the same. However, Latin America and many European nations still have separate flags for tradition reasons.
Many countries also have naval ensigns and battle flags. These flags are used by navies and armies. The most well known battle flag has to be that of the Confederate States of America. The well known flag was also the jack for two of the national flags but was never the national flag for the Confederacy. However, its use in battle and reuse in reenactments has embedded it as the symbol of rebellion in many people's mind. This has led to the confusion over its historical meaning.