Role of a Test Engineer ? : Finding and reporting bugs that a customers/hackers can find (period).
Bug ?: Any deviation from expected outcome for a given action. Expected outcome is defined based on production Requirement Document (or, it’s derivatives)
Functional Testing ? : Testers will normally represent single user and exercise various functionality offered by product.
Browser compatibility ? : Part of functionality test cases that was executed on various OS/Browser combination to verify that it works on all or, major players
Performance ?: Tester tries to benchmark product for best numbers against given server configuration. One should make sure to minimize impact of external factors like network latency, other processes on server , client bottleneck etc.
Reliability? : Run some chosen test scenario for long duration (24 hrs to weeks) . This helps in detecting resource leaks.
Scalability?: Scaling different attribute of product to find their limits.
Stress? : product response under extreme load on Server ( The load could be on cpu cycle, memory due to other code running on system)
L10N?: Localization testing : – Testing product to verify that it supports localized language.
i18n?: Internationalization testing. — Testing code for localization readiness.
Many more one liner definition to come with time…..