The client startup chain is the ordered set of components, checks, and dependencies an application must pass before it opens successfully. It can include the launcher, signed binaries, configuration files, libraries, authentication steps, hardware checks, and runtime services. If any link in that chain fails, the app may crash, hang, or never appear on screen.
This matters in cyber security because attackers and defenders both care about startup behavior. A malicious change to a DLL, package, script, or environment setting can break the chain and cause denial of service, or redirect execution into untrusted code. Defenders use the same concept to troubleshoot launch failures, verify file integrity, compare app and OS versions, and isolate whether a problem is in the operating system, the application package, or a device-specific compatibility path.