Wikipedia
Telco-OTT (Over-The-Top) is where a telecommunications service provider delivers one or more services across an IP network. The IP networks is predominantly the public internet although sometimes telco-run cloud services delivered via a corporation's existing IP-VPN from another provider, as opposed to the carrier's own access network. It embraces a variety of telco services including communications (e.g. voice and messaging), content (e.g. TV and music) and cloud-based (e.g. compute and storage) offerings.
Stimulated by the availability of high performance fixed and mobile broadband networks as well as the rapid adoption of smartphones and tablet computers, telco-OTT is viewed by a selection of industry analysts and media commentators as the mechanism that mobile network operators need to employ in order to compete with the vast and growing range of over-the-top (OTT) services provided by non-telco companies.
Telco-OTT is a response to the fact that users will have multiple devices ( smartphones, laptops or other connected devices such as TVs, games consoles) which almost inevitably will have various different access providers (especially with the growth of public-access Wi-Fi). So to deliver consistent telco-branded services, at some points at least, they will need to be delivered over 3rd-party access.
The term was first coined by telecoms industry analyst Dean Bubley who first published a report on it in February 2012, but first used the term in a June 2011 presentation he gave at the eComm conference in SF.