Trad jazz - short for "traditional jazz" - refers to the Dixieland and Ragtime jazz styles of the early 20th century in contrast to any more modern style. - Text from: Wikipedia-Trad Jazz

A Dixieland revival began on the west coast in the late 1930s as a backlash to the Chicago style, which was close to swing. Lu Watters and the Yerba Buena Jazz Band, and trombonist Turk Murphy, adopted the repertoire of Joe "King" Oliver, Jelly Roll Morton, Louis Armstrong and W.C. Handy: bands included banjo and tuba in the rhythm sections. A New Orleans-based traditional revival began with the later recordings of Jelly-Roll Morton and the rediscovery of Bunk Johnson in 1942, leading to the founding of Preservation Hall in the French Quarter during the 1960s. - Text from: Wikipedia-Trad Jazz

Early King Oliver pieces exemplify this style of hot jazz; however, as individual performers began stepping to the front as soloists, a new form of music emerged. Ironically, one of the ensemble players in King Oliver's Creole Jazz Band, Louis Armstrong, was by far the most influential of the soloists, creating, in his wake, a demand for this "new" style of jazz, in the late 1920s and early 1930s. Other influential stylists who are still revered in traditional jazz circles today include Sidney Bechet, Bix Beiderbecke, Wingy Manone and Muggsy Spanier. Many artists of the Big Band era, including Glenn Miller, Gene Krupa and Benny Goodman, had their beginnings in trad jazz. - Text from: Wikipedia-Trad Jazz

Trad in Britain

In Britain, where boogie-woogie, "stride" piano and jump blues were popular in the 1940s, the Humphrey Lyttelton band pioneered a trad revival just after the Second World War, and Ken Colyer's Crane River band added a strong thread of New Orleans purism. During the 1950s and well into the 60s Chris Barber, Terry Lightfoot, Acker Bilk, George Chisholm, Kenny Ball, Mick Mulligan and Mike Cotton - who "went R'n'B". in 1963-4 - made regular appearances live, on the air and in the British charts, as did Louis Armstrong himself. More light-hearted versions were offered by The Bonzo Dog Doo-Dah Band, The Temperance Seven and The New Vaudeville Band. Dixieland stylings can be found here and there on records by The Rolling Stones, The Beatles, The Small Faces and The Kinks, while The Who actually performed trad jazz in their early days. - Text from: Wikipedia-Trad Jazz

It was Chris Barber whose band performances gave a stage to Lonnie Donegan and Alexis Korner, setting off the craze for skiffle and then British rhythm and blues that powered the Beat boom of the sixties. - Text from: Wikipedia-Trad Jazz

Later revivals

Following a revival of interest in the late 1980s, a number of musicians such as Wynton Marsalis began performing and recording not only original trad jazz tunes but new compositions in the style as well. - Text from: Wikipedia-Trad Jazz