# What do the terms milli-g and microgravity mean? How are they used?

I've seen the terms "milli-g" acceleration and microgravity in many questions and answers here, within the context of spaceflight.

Does milli-g refer to accelerations between 0.001 $g_0$ and 1 $g_0$, and microgravity to those between 1E-06 $g_0$ and 0.001 $g_0$, or does the usage of the terms really refer to the underlying concept or application?

uses of milli-g:

uses of microgravity:

• While microgravity is easily google-able finding this link quite quickly. I however was unable to tell whether milli-g stands for "milli-g uni" as highlighted in your question or "milli-gram force". I've left a comment so someone with more knowledge can use it as a stepping stone as I don't have the expertise to complete an answer. – Edlothiad Mar 16 '18 at 7:32
• @Edlothiad I'm asking of course about their specific usage in spaceflight. Edited to make that clearer. – uhoh Mar 16 '18 at 8:13
• As far as I can tell, that wouldn't change any of the information in my comment above. Microgravity remains as a general word for very, low-gravity situations, where as milli-gs appear to be a unit regardless if it's in spaceflight or in underwater propulsion. Unless I'm missing something..? – Edlothiad Mar 16 '18 at 8:16
• @Bear I think it's used when acceleration is very small but can not or at least should not be neglected. – uhoh Mar 16 '18 at 15:12
• @OrganicMarble How about "microacceleration with respect to a potentially rotating local frame"? Doesn't exactly roll off the tongue though – uhoh Mar 16 '18 at 15:32