Update glossary.md

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@@ -4,7 +4,7 @@ TODO
 
 Naming things is hard. This page tries to reduce confusion around naming.
 
-## Fuzz Target**
+## Fuzz Target
 Or **Target Function** or **Fuzzing Target Function**.<BR>
 A function to which we apply fuzzing.
 A [specific signature](libfuzzer.info#fuzz-target) must be used for OSS-Fuzz.
@@ -14,4 +14,30 @@ Examples: [openssl](https://github.com/openssl/openssl/blob/master/fuzz/x509.c),
 A Fuzz Target can and should also be used for regression testing
 and for reproducing bug reports, see [ideal integration](ideal_integration.md).
 
-* **Fuzzing Engine** a program that tries to find interesting inputs 
+## Fuzzing Engine
+
+A program that tries to find interesting inputs for a Fuzz Target by executing it.
+Examples: [libFuzzer](http://lbfuzzer.info),
+[AFL](lcamtuf.coredump.cx/afl/),
+[honggfuzz](https://github.com/google/honggfuzz), etc 
+
+See also [#mutation-engine] and [#test-generator].
+
+## Test Input
+Or **reproducer**, or **testcase**. 
+A sequence of bytes that is used as the input to a Fuzz Target. 
+
+## Mutation Engine
+A tool that take a set of testcases
+and creates their mutations, but do not directly feed the mutations to Fuzz Targets.
+Example [Radamsa](https://github.com/aoh/radamsa),
+
+## Test Generator
+A tool that generates testcases 
+
+## Fuzzer
+
+The most overloaded term, which makes it bad (maybe, we should try avoiding it?).
+Sometimes the "Fuzzer" is referred to a Fuzz Target, sometimes to a Fuzzing Engine, Mutation Engine, or a Test Generator. 
+Sometimes to a binary built from a Fuzz Target using some of the Fuzzing Engine and optionally with some dynamic testing tool. 
+