K-line may refer to:

Chemistry

K-line (spectrometry), one of two features in spectroscopy:

• Calcium K line, a Fraunhofer spectral line from ionised calcium

• K-line (x-ray), an x-ray peak in astronomical spectrometry

  K line, a term used in Internal conversion electron spectroscopy

Computing

• K-line (artificial intelligence) (Knowledge-line), a mental agent in artificial intelligence

• K-line (IRC), a server ban in IRC

Finance

• Candlestick chart, or K-line, a style of financial chart used to describe price movements of a security, derivative, or currency

Sports

• K line, the line marking the calculation point in ski jumping

Transportation

• K (Broadway Brooklyn Local), earlier KK, discontinued in 1976

• K (Eighth Avenue Local), a defunct train service on the New York City Subway, which was known as the AA until 1985

• K Ingleside, a service of the San Francisco Municipal Railway sometimes called the K Line

• K Line (Los Angeles Metro), a light rail line in Los Angeles County, California

• K (Los Angeles Railway), defunct streetcar line in Los Angeles, California

• K Line, a Japanese shipping company

• K-Line, a model railway locomotive company

• K-Line bus operator in Yorkshire, England since rebranded as Tiger Blue

• Line K (Tren Interoceánico), a planned railway service in Mexico

• K-Line, part of the ISO 9141 on-board diagnostics vehicle network interface standard