Definition of Merseyside Derby

What is the "Merseyside Derby"? What does the term "Merseyside Derby" mean as it applies to the world of football?

Merseyside Derby is a football match between Everton and Liverpool. It is the longest running top flight derby in England and it has been played since 1962/63. Merseyside Derby is the only derby in England where total fan segregation is not enforced. A lot of families in the city of Liverpool have both Everton and Liverpool supporters in them and the match between these two teams is sometimes referred to as the friendly derby.

Lately, since the mid 1980's, the tension between the two teams has increased on and off the field and now the Merseyside Derby on average has more red cards than any other English Premier League match.