Program temporary fix

In IBM terminology a Program temporary fix or Product temporary fix (PTF), sometimes depending on date, is a single bug fix, or group of fixes, distributed in a form ready to install for customers.
A PTF normally follows an APAR (Authorized Program Analysis Report), and where an "APAR fix" was issued, the PTF "is a tested APAR" or set of APAR fixes. However, if an APAR is resolved as "Fixed If Next" or "Permanent Restriction" then there may be no PTF fixing it, only a subsequent release.
PTF usage.
PTFs used to be distributed in a group on a so-called "Program Update Tape" ("PUT") or "Recommended Service Upgrade" ("RSU"), approximately on a monthly basis. They can now be downloaded straight to the system through a direct connection to IBM support. In some instances IBM will release a "Cumulative PTF Pack", a large number of fixes which function best as a whole, and are sometimes codependent. When this happens, IBM issues compact discs containing the entire PTF pack, which can be loaded directly onto the system from its media drive. 
One reason for the use of physical media is size, and related (default) size limits. "By default, the /home file system on VIOS (Virtual I/O Server) for System p is only 10GB in size." If the "Cumulative PTF Pack" is larger than the default, "If you try (to) FTP 17GB of ISO images you will run out of space."
The PTFs are processed using SMP/E (System Modification Program/Extended) in several stages over a course of weeks.
If the system is adversely affected by the PTF, a system administrator may sometimes "reject" (un-apply) the PTF and seek further support from IBM. However, if no problems are found after the PTF is applied, it can be permanently installed, "accepted", or "committed", to the system.
These repairs to IBM software are often in response to APARs submitted by customers and others and acted on by IBM, and are a common first step to resolving software errors. It is generally expected by the customer that the problem would be fully corrected in the next release (version) of the relevant product.
Comparison to APAR.
At times IBM software has a bug. 
Once IBM has ascertained that the cause is not one of
IBM support staff, if they suspect that a defect in a current release of an IBM program is the cause, will file a formal report confirming the existence of an issue. This is referred to as an "Authorized Program Analysis Report (APAR)." See 
APARs also include
Summary.
There are at least 2 levels of fix:
The focus of the "APAR fix" is "to rectify the problem as soon as possible" whereas the PTF "is a tested APAR... The PTF 'closes' the APAR. " Prior to that, an APAR is "a problem with an IBM program that is formally tracked until a solution is provided.”
Humor.
Customers sometimes explain the acronym in a tongue-in-cheek manner as "permanent temporary fix" or more practically "probably this fixes", because they have the option to make the PTF a permanent part of the operating system if the patch fixes the problem.