What term describes clothing or accessories that remain timeless and never go out of fashion?

The term that describes clothing or accessories that remain timeless and never go out of fashion is "classic." Classic items are characterized by their enduring appeal and ability to withstand the test of time, often becoming staples in a wardrobe due to their versatility and elegance. Classic designs are typically simple and clean, making them appropriate for various occasions and styles, which is why they are consistently sought after, regardless of fleeting fashion trends.

In contrast, trendy items are those that reflect the latest fashions which can change rapidly, while avant-garde refers to innovative or experimental styles that may be ahead of their time but are not necessarily timeless. Contemporary fashion reflects current styles and aesthetics, but like trendy pieces, it can also change quickly with evolving tastes. This distinction highlights why "classic" is the most suitable term for describing clothing and accessories that maintain their relevance over time.