a trend that is currently fashionable, a popular cause, party, or function, or something that generally has widespread support (often used in the phrase "jump on the bandwagon");
e.g. Many companies have jumped on the bandwagon of using holidays to promote sales.
(noun)
a high wagon, usually with ornate decoration, used for carrying a band of musicians in a procession or parade;
e.g. Everyone cheered as the bandwagon passed by, carrying the musicians and followed by dancers.