Definition of "density"

In the past two years, NASA’s Kepler Space Telescope has located nearly 3,000 exoplanet candidates ranging from sub-Earth-sized minions to gas giants that dwarf our own Jupiter. Their densities range from that of styrofoam to iron.

2013 May-June, Kevin Heng, “Why Does Nature Form Exoplanets Easily?”, in American Scientist, volume 101, number 3, page 184

Aquafaba was recovered from 10 commercial canned chickpea products and correlations among aquafaba composition, density, viscosity and foaming properties were investigated. Proton NMR was used to characterize aquafaba composition before and after ultrafiltration through membranes with different molecular weight cut offs (MWCOs of 3, 10, or 50 kDa).

2018 October 3, Youn Young Shim, Rana Mustafa, Jianheng Shen, Kornsulee Ratanapariyanuch, Martin J. T. Reaney, “Composition and Properties of Aquafaba: Water Recovered from Commercially Canned Chickpeas”, in Journal of Visualized Experiments‎, volume 132

Density, which is genetically linked, deals with the number of strands per square inch on your scalp. Normal density can range from slight to substantial, varying from person to person.

2007, Lisa Akbari, Every Woman's Guide to Beautiful Hair at Any Age‎, page 37

It is vital to use proper keyword density because if your density is too low, your SERP's ranking decreases.

2010, Alyssa Ast, The Fundamentals of SEO for the Average Joe‎, page 23

Let's say you get a new customer across town and you don't have any other customers over there. You still need to be competitive with price, but it costs too much money to send crews or a serviceman to one account across town. You need to get more customers over there for margins to exceed the costs of going over there. Once you hit a certain density, you're in the black.

2010, Neil Gillespie, Discover Your Core, Then Go for More‎, page 42