The entire policy can be found here, and the Cliff Notes version is below:
Who controls your information?
Twitter, Inc in San Francisco controls your information if you’re in the USA and Twitter International, an Irish company, controls it if you’re located outside of the United States. However, regardless of which organization captures your data, they can “transfer, store and use” it in any country they operate in. (Which is basically anywhere on the planet with Internet access).
Twitter says, “We collect and use your information to provide, understand and improve services.”
Public Account Information:
You can create and manage multiple Twitter accounts, for example multiple brand and personal or executive accounts such as Partner-facing and corporate Twitter handles.
Your name and username are always listed publicly and accessible via Twitter search
You can use a pseudo name instead of your actual name if you want but it’s still publicly searchable
Providing a phone number is your agreement to receive texts
Your email is used for updates, marketing and to help others find your account
Email can also be used for the same purposes by their third party services mentioned above as well as these corporate affiliates:
Note: Don’t want to be found by phone and/or email? You can control this in the discoverability settings of your account.
If you allow Twitter (or their other services) access to your contacts, they will help you find them in order to connect. Twitter “may” also use that information to personalize the content they send to you such as suggestions for other connects.
Note: If you already uploaded your contact list but don’t want them to use it in this way; change your preferences here.
Tweets, Following, Lists, Profile and Other Public Information:
Twitter collects metadata about your activities including:
What time you created a Tweet
Your language, country, and time zone
Lists you create
People you follow
Tweets you like and retweet
Broadcasts that your liked on Periscope that you also engage with on Twitter
When you publish a Tweet or add/change your profile, this is where that public information instantly goes:
Developers and publishers that integrate Twitter content into their services
Universities, public health agencies, market researchers and others who analyze it for trends and draw insights from your data
Warning from Twitter: Before posting, think carefully about how public you want that information to become.
How Twitter may uses non-public data:
For direct messaging, Twitter says they “store and process your communications and information related to them” Vague, right? Yes – so just understand a private message on Twitter might not be so private after all.
Other ways - Twitter uses your data to:
Track your location in order to serve up local content via GPS, IP addresses, and nearby cell towers
Track how you interact with links on their platform – including any links included in non-public areas like direct messages
Make advertising more relevant to you (note: within Personalization and Data settings you can determine ad categories you want to see
Gather information from all your devices to serve you content they believe will be of interest
Gather information about your devices including ANY desktops, laptops and mobile devices you use or have used to log into Twitter so, if you're managing executive or Partner-facing Twitter accounts from home devices, it's a good idea to change these settings especially if you don't want your teenager's preferences applied to Twitter accounts you manage for work!