OTA means "over the air". That simply means that your Ubuntu Phone service provider is updating your phone software instead of like with a desktop where you would manage your software upgrades. This is likely a whole operating system upgrade or collection of core software rather than applications from an app store.
Canoical's Łukasz Zemczak has sent in his report on the work done by
the Ubuntu Touch developers in preparation for the seventh OTA
(Over-the-Air) software update for the mobile operating system.
According to Mr. Zemczak, things are calming down in the Ubuntu Touch
world, as the last remaining bugs to be implemented in the OTA-7
update have been fixed, along with various other minor changes.
Therefore, the developers have already started to build the re-spin
images, perform sanity checks, as well as delta testing.
If the testing results are OK, the Ubuntu Touch OTA-7 images will be
sent to phone manufacturers, in this case BQ and Meizu, for the final
check. Then, Canonical will start uploading the OTA-7 images to the
official mirrors and send the update to all Ubuntu phone users, which
will happen sometime in the first half of next week.
"The (hopefully) final OTA-7 re-spin is in progress with the two
blocking issue fixed and changes released. Big thanks to everyone
involved," said Łukasz Zemczak. "Once the image is built QA will
perform sanity and delta testing on the generated images and if
everything is ok, the image will then go to manufacturers for a final
check. ETA for release: first half of next week."
So we see that in this case it's the 7th update of this sort.
Trying to explain it on simple terms it may be tempting to compare an OTA (Over-the-Air) software update to a Service Pack for modern devices:
In computing, a service pack or SP (in short SP) or a feature pack (FP) comprises a collection of updates, fixes, or enhancements to a software program delivered in the form of a single installable package. Companies often release a service pack when the number of individual patches to a given program reaches a certain (arbitrary) limit, or the software release has shown to be stabilized with a limited number of remaining issues based on users' feedback and bug tracking such as bugzilla. In large software applications such as office suites, operating systems, database software, or network management, it is not uncommon to have a service pack issued within the first year or two of a product's release. Installing a service pack is easier and less error-prone than installing many individual patches, even more so when updating multiple computers over a network, where service packs are common.
The difference is that with modern devices most of these are not installer based like Windows Installer or individual apps but (filesystem) image based, which means your devices main filesystem (root) will be overwritten with the new image instead of tediously checking if a file exists and needs updating or not. To save bandwidth and writes to the flash memory mechanisms like delta updates are used, which works under the assumption that this particular filesystem is in pristine condition, not modified by someone else and on a specific version that is eligible for a (delta) update. Which is why you shouldn't use desktop package management software like APT on these devices, because it will either revert all changes made or lead to an unstable system (bricked!).
OTA means "over the air". That simply means that your Ubuntu Phone service provider is updating your phone software instead of like with a desktop where you would manage your software upgrades. This is likely a whole operating system upgrade or collection of core software rather than applications from an app store.
From Softpedia:
So we see that in this case it's the 7th update of this sort.
An over-the-air update (OTA update) is the wireless delivery of new software or data to mobile phones and tablets.
Source: http://searchmobilecomputing.techtarget.com/definition/OTA-update-over-the-air-update
Trying to explain it on simple terms it may be tempting to compare an OTA (Over-the-Air) software update to a Service Pack for modern devices:
The difference is that with modern devices most of these are not installer based like Windows Installer or individual apps but (filesystem) image based, which means your devices main filesystem (root) will be overwritten with the new image instead of tediously checking if a file exists and needs updating or not. To save bandwidth and writes to the flash memory mechanisms like delta updates are used, which works under the assumption that this particular filesystem is in pristine condition, not modified by someone else and on a specific version that is eligible for a (delta) update. Which is why you shouldn't use desktop package management software like APT on these devices, because it will either revert all changes made or lead to an unstable system (bricked!).