What is the proper term for the lowest natural frequency that is produced by a vibrating object, such as an instrument?

i believe your looking for this word ?? "fundamental".

Fundamental frequency

Explanation:

Fundamental frequency is the lowest frequency which produced due to the oscillation of the body. This frequency is different from other higher frequencies.  If the tube is closed at one end, the velocity of sound divided by 4 times the length of the tube gives the fundamental frequency. The higher frequencies can be obtained by integral multiple of the fundamental frequency.

"i have always loved contemporary art and made it a general goal to work within the field. after a few nonprofit internships at museums and galleries, i decided to try the for-profit art world and was offered a job as the ad assistant at the magazine. i much prefer the pace of the for-profit art community and have stayed with the company for three years, with a promotion to an account manager last spring."

i just did this and got a 100.