TPM is a chip that is included on higher end business-oriented computers. If present, it is used by BitLocker.
If you don’t have TPM in your computer, you can still use BitLocker if you follow the steps below (from a post on answers.microsoft.com ).
How to Configure Computer to Enable BitLocker without Compatible TPM:
Administrators must follow the steps below to configure their Windows 8 computers to allow enabling Bit Locker Drive Encryption without compatible TPM:
a. Log on to Windows 10 computer with an account that has administrative privileges.
b. Assuming that the computer has been configured to display the classic start menu, click Start (or the Windows icon) and at the bottom of the menu in search box type GPEDIT.MSC command and press enter key.
c. On the opened Local Group Policy Editor snap-in, from the left pane expand Computer Configuration > Administrative Templates > Windows Components > Bit Locker Drive Encryption and from the expanded list click to select Operating System Drives.
d. From the right pane double-click “Require additional authentication” at startup.
e. On the opened box click to select Enabled radio button and ensure that under Options section Allow Bit Locker without a compatible TPM checkbox is checked.
f. Once done, click Ok button to allow the changes to take effect and close Local Group Policy Editor snap-in.