infill

"Infill" is a flexible word built around one clear idea: filling a gap or empty space so something becomes more complete, supported, or useful. It is most common in practical and technical fields, especially construction, urban planning, and 3D printing.

In its older and more physical sense, "infill" can mean material such as soil, rock, sand, or concrete that is used to fill a hole, raise ground level, or support a structure. If a site has been dug out or left uneven, infill may be added to make the surface stable and usable again.

In modern urban planning, infill development has become a key concept for sustainable growth. It refers to building on vacant or underused land within existing urban areas. By revitalizing these "gaps" in the city fabric, planners can increase density and utilize existing infrastructure rather than allowing cities to sprawl into undeveloped countryside.

The term is equally important in the digital realm, specifically in 3D printing. Because printing a completely solid object is often wasteful, software uses "infill patterns" (like honeycombs or grids) to create an internal support structure. A higher infill percentage results in a denser, heavier, and stronger object, while a lower percentage saves time and material.

Less often, the word can be used more broadly for filling a missing part, but that use is much less common than the physical and technical meanings. In everyday English, you are far more likely to see "infill" in discussions about land use, construction material, or the inner structure of a printed object. Whether it is soil packed into a gap, a new building on an empty city lot, or a grid pattern inside a 3D-printed part, "infill" keeps the same basic sense: something fills space within an existing shape or area.