AIML stands for Artificial Intelligence Markup Language. It's an XML-based language designed by Dr. Richard Wallace in 2001 for development of the A.L.I.C.E. chatbot.
<aiml version="1.0">
<!-- Basic atomic trigger/response -->
<category>
  <pattern>HELLO BOT</pattern>
  <template>
    Hello, human.
  </template>
</category>
<!-- Wildcard, variable learning, random replies. -->
<category>
  <pattern>MY NAME IS *</pattern>
  <template>
    <think><set name="name"><formal/></set></think>
    <random>
      <li>It's nice to meet you, <get name="name"/>.</li>
      <li>Nice to meet you, <get name="name"/>.</li>
    </random>
  </template>
</category>
<!-- Redirect (alias) one pattern to another. -->
<category>
  <pattern>CALL ME *</pattern>
  <template>
    <srai>MY NAME IS <star index="1"/></srai>
  </template>
</category>
<!-- Conditions -->
<category>
  <pattern>WHAT IS MY NAME</pattern>
  <template>
    <condition name="name">
      <li value="undefined">You never told me your name.</li>
      <li>Your name is <get name="name"/>, seeker!</li>
    </condition>
  </template>
</category>
</aiml>
See RiveScript vs. AIML for the language and syntax differences between RiveScript and AIML.