IPC-A-610 for PCB fabrication and IPC-J-STD-001 for assembly acceptance use 3 classes to define solder joint goal acceptability for various electronic products.

CLASS 1 – General Electronic Products

Includes products suitable for applications where the major requirement is function of the completed assembly. Toys

CLASS 2 – Dedicated Service Electronic Products

Includes products where continued performance and extended life is required, and for which uninterrupted service is desired but not critical. Typically, the end-use environment would not cause failures. Computers & Phones

CLASS 3 – High Performance Electronic Products

Includes products where continued high performance or performance-on-demand is critical, equipment downtime cannot be tolerated, end-use environment may be uncommonly harsh, and the equipment must function when required, such as life support or other critical systems. Military & Medical 

The J-STD-001 and the 610 standards are broken down into these definitions:

N = No requirement has been established for this Class

A = Acceptable

P = Process Indicator

D = Defect

Examples:

[A1P2D3] is Acceptable Class 1, Process Indicator Class 2 and Defect Class 3

[N1D2D3] is Requirement Not Establish Class 1, Defect Classes 2 and 3

[A1A2D3] is Acceptable Classes 1 and 2, Defect Class 3

[D1D2D3] is Defect for all Classes

A defect for a Class 1 product means that the characteristic is also a defect for Class 2 and 3. A defect for a Class 2 product means that the characteristic is also a defect for a Class 3 product, but may not be a defect for a Class 1 product where less demanding criteria may apply.

Defect = Non-conformance to the requirements of this standard or other risk factors as identified by the manufacturer.

Process Indicator = A detectable anomaly, other than a defect, that is attributable to variation in material, equipment operation, workmanship or processes.

For additional information about how IPC compliance affects Footprint Land Patterns in Library Expert and Altium Designer read these posts: 

http://https://www.pcblibraries.com/forum/paste-mask-rules-for-thermal-pads_topic2452.html" rel="nofollow - Thermal Pads

http://https://www.pcblibraries.com/forum/ipcjstd001-chip-component-solder-joints_topic2588.html" rel="nofollow - Chip Solder Joints

http://https://www.pcblibraries.com/forum/ipcjstd001-gull-wing-leads-and-solder-joints_topic2587.html" rel="nofollow - Gull Wing Terminal Leads

http://https://www.pcblibraries.com/forum/who-is-ipc-and-how-do-they-affect-pcb-libraries_topic2584.html" rel="nofollow - Who is IPC?