Basically the difference between <frame> tag and <iframe> tag is :
When we use <frame> tag then the content of a web page constitutes of frames which is created by using <frame> and <frameset> tags only (and <body> tag is not used) as :
<html>
<head>
<title>HTML Frames</title>
</head>
<frameset rows="20%,70%,10%">
<frame name="top" src="/html/top.html" />
<frame name="main" src="/html/main.html" />
<frame name="bottom" src="/html/bottom.html" />
</frameset>
</html>
And when we use <iframe> then the content of web page don't contain frames and content of web page is created by using <body> tag (and <frame> and <frameset> tags are not used) as:
<html>
<head>
<title>HTML Iframes</title>
</head>
<body>
<p>See the video</p>
<iframe width="854" height="480" src="https://www.youtube.com/embed/2eabXBvw4oI"
frameborder="0" allowfullscreen>
</iframe>
</body>
</html>
So <iframe> just brings some other source's document to a web page. The <iframe> are used to specify inline frames or floating frames. The World Wide Web Consortium (W3C) included the <iframe> feature in HTML 4.01.
<frameset> tags were used to create frames with the tag <frame> whereas <iframe> fulfills functions of both <frame> and <frameset> tags. Unlike <frame> tags, <iframe> tags can also be placed inside the <body> tags.
Placement of <iframe> is easy, a coder can easily put the <iframe> tag among the other webpage tags, and also add several <iframe> tags if he/she wants. On the other hand, placing <frame> tags in <frameset> is bit complicated.
Note : <frame> tag and <frameset> tag are deprecated in HTML5
So now as use of <frame> and <frameset> tag is deprecated so web developers use <body> tag for creating content of a webpage and for embedding some other source's document in the web page <iframe> tags are used. But even <frame> tags were also used to embed other source's document in a webpage and even <iframe> tags are also used to create frames.