This phrase means "Always Faithful" or "Always Loyal" in Latin. As a laconic and meaningful phrase, expressing loyalty and pride, it is used by many countries and organizations as a motto.

It is known in the USA as the official motto of the United States Marine Corps. Many towns and families in England and Ireland have been using the phrase as a motto since the 15th century. The first recorded use of the phrase is the motto of Abbeville, a French town, which used Semper Fidelis back in 1369.

More Info: en.wikipedia.org