Big Bertha
Big Bertha is a euphonious term for an unusually large example of a class of object; notable examples include:

Military guns

 Big Bertha (howitzer), a heavy mortar-like howitzer built and used by Germany during World War I
 Paris Gun, called Big Bertha by the French, and several other big heavy German guns of World War I

Vehicles

MR 0-10-0 Lickey Banker, a large railway banking engine, especially of a 0-10-0 steam locomotive configuration
A special version of the Vauxhall Victor automobile

Fictional characters

Big Bertha (comics), a Marvel Comics superhero
 Big Bertha, an "abnormal" in the Sanctuary television series
 Big Bertha, a recurring enemy in the Mario franchise - see Characters in the Mario franchise

Other uses

Big Bertha (lunar sample), the third largest lunar rock collected by the Apollo program during Apollo 14
Bertha Heyman, a.k.a. "Big Bertha", a 19th-century criminal
Big Bertha (cow), a cow that broke two Guinness World Records, for being both the oldest and having the most offspring
Big Bertha (golf club), a line of golf clubs from Callaway Golf
Big Bertha (drum), one of the world's largest bass drums
IBM T220/T221 LCD monitors, nicknamed Big Bertha, LCD monitors with a native resolution of 3840×2400 pixels
Bertha (tunnel boring machine), nicknamed Big Bertha, a tunnel boring machine
La Grosse Bertha (French for "Big Bertha"), a French satirical magazine