Terminology index - a list of bike part names and cycling concepts
Bicycle-Shaped Object (BSO)
A derogatory term for a very cheaply produced bike with very low quality components. The components can be hard to maintain due to poor tolerances. BSOs are often sold at non-specialty retail stores.
The etymology of the term is uncertain. It appears in use in some parts of the English-speaking world. It may originate in the UK, as discussed at the link. Other languages may use terms equivalent to supermarket bike or department store bike. These terms are likely to be understood in English as well.

For instance the BSO pictured is being sold in the UK by ASDA (owned by Walmart) for £75. These bikes tend to be mass produced and sold in flat pack boxes for self-assembly.
Purchasers of lower-end bicycles tend to be less experienced cyclists who focus on price. Many BSOs carry features which are included for marketing purposes but are unnecessary for the typical end-user. Such features may include front and rear suspension, wide off-road style tyres and an excessive number of gear ratios. For cyclists who are riding on city streets or smooth trails, these features are unnecessary. Including these features reduces the budget available for better components elsewhere.
It is more advisable to search for a cheap second-hand bike in a similar price range from a more experienced cyclist or on eBay than to go for one of these.