In North America, it's considered a rivalry. In Europe the more commonly used word is 'derby'. No matter what you call it, these are some of the most intense, storied battles in all of European football today.
El Clasico: Real Madrid v FC Barcelona (Spain)
These Spanish powerhouses have been squaring off since 1929. Of the 226 official matches played, Madrid holds slim margin of victory at 90-88-48. Expect this one to stay hotly contested for years to come.
North-West Derby: Manchester United v Liverpool (England)
This storied rivalry didn't need anymore build up. Yet, after the Luis Suarez racism issue with Patrice Evra, things only heated up for the two red sides. United holds a 75-51-64 record in the derby, but this season has given Liverpool some extra bragging rights.
De Klassieker: Ajax v Feyenoord (Netherlands)
The Amsterdam/Rotterdam feud is one of Europe's uglier ones. In 1997 an Ajax fan died in a violent battle between rival support groups. This resulted in an away match ban for supporters of both sides that season. In 2005, a new away match ban of five years was installed to curb violence. On the pitch Ajax leads with a record of 78-55-42.
Old Firm Derby: Celtic v Rangers (Scotland)
This rivalry started in 1888 and carries significance well beyond football. Issues ranging from religion to social identities hang over the two most storied clubs in the league during this one. With 399 matches between them, Rangers lead with 159 wins to Celtic's 144.
Revierderby: Borussia Dortmund v Schalke 04 (Germany)
Germany's most well-known derby pits the Ruhr region's top clubs against one another. Schalke holds the lead at 56 wins of the 142 matches played. Yet, in recent years Jurgen Klopp's side have become a European force that should be evening the series sooner than later.
Milan Derby: AC Milan v Inter Milan (Italy)
Milan bragging rights are on the line in this clash. Bragging rights to the famous San Siro stadium are at stake as well, as these two share the grounds. It's like the Giants vs the Jets except they have a close record. Out of 212 matches, Inter holds a narrow 76-74 lead in wins.
North London Derby: Arsenal v Tottenham Hotspur (England)
While Arsenal tends to dominate (76-54-47), that doesn't make the battle any less heated. With Tottenham's slight resurgence in the past few years the two have been competing for the last remaining Champions League slot quite a few times. Keep hope alive, Spurs!
Kitalararasi Derbi: Galatasaray v Fenerbahce (Turkey)
These Turkish powerhouses have been battling for over a century now, as have their supporters. On the pitch, the battle is no less heated between the sides separated by the Bosphorus. The Asian side of Turkey (Fenerbahce) holds the lead over their European side at 143-121-113.
Derby D'Italia: Juventus vs. Inter (Italy)
Northwest Italy's largest cities square off in this historic battle. Not only are the cities large, but so are both clubs' histories. Juve also holds a large lead as they control the derby 94-67-53. Advantage, Turin.
Merseyside Derby: Everton v Liverpool (England)
This battle has been raging since 1894. Since 1962, the clubs have met every year- making this England's longest running derby to date. Judging from wins, Everton has lost control of the city to its red counterparts. Liverpool leads 89-66-67.
O Clássico: Benfica v Porto (Portugal)
This battle pits two of the country's top three clubs (Sporting being the other) against one another. Like several others on the list, this extends into Portugal's cultural and political classes as well. The clubs from rival affluent cities hold a close record, with Porto just ahead, holding 88 victories to Benfica's 85.
Der Klassiker: Bayern Munich vs. Borussia Dortmund (Germany)
While not as storied as others (Only 100 matches played) these two German powerhouses have been likened to El Clasico in recent years. Bayern holds the lead with 43 wins to Dortmund's 28. This gap may widen with Dortmund star Robert Lewandowski's upcoming summer transfer to Bayern.
Manchester Derby: Manchester City v Manchester United (England)
While United holds a convincing lead (69-48-50) over its city rival, the gap could be closing in the coming campaigns. New ownership has made City a perennial contender in the EPL, including an incredible last minute goal to steal the 2012 title from United. If United continues backsliding in the wake of Sir Alex Ferguson's retirement, the record could balance out in time.
Derby Della Capitale: Lazio v Roma (Italy)
The country's hottest inter-city rivalry takes place in the capital. Roma's more consistent form shows in the records as they have taken 58 wins from 190 official matches. Lazio has some work to do with just 42.
The Derby of the Eternal Enemies: Panathinaikos v Olympiakos (Greece)
What is arguably the greatest moniker of all the derbies, this Athens battle pits wealth (Panathinaikos) against the working class (Olympiakos). The clash has remained heated despite a lopsided lead for the working class heroes. Olympiakos holds a commanding record of 76-47-66.