What is the difference between a glide and a semivowel?

Question

Is the following distinction made by this university lesson between glides and semivowels standard?:

Glides include speech sounds where the airstream is frictionless and is modified by the position of the tongue and the lips. Glides and semivowels are very similar to vowels. The difference between vowels and glides and semivowels lies in the structure of the syllable. Vowels occur at the peak of the syllable--the most sonorous part of the syllable. Glides immediately precede a vowel; they are less sonorous than the vowel they precede. Semivowels immediately follow a vowel in the syllable. These too are less sonorous than a vowel. Glides tend to be 'stronger' than semivowels. There are two basic glides/semivowels:

1. palatal, high unrounded: "y" as in yes and in boy
2. labial, high rounded: "w" as in win and cow

Answer 1

No. In the vast majority of contexts, glide and semivowel are synonymous. See e.g. Ladefoged & Johnson (2015: 191), Rogers (2000: 184), Ball & Rahilly (1999: 51).

Definitions of glide that somewhat differ from that of semivowel are sometimes encountered (e.g. Catford 2001: 68, Crystal 2008: 211), but even they don't match the definition in your source.

In fact, semivowels that precede the vowel that's the peak of the syllable and ones that follow it—i.e. "glides" and "semivowels" according to your source—are sometimes referred to respectively as on-glides and off-glides. (Note, though, that on-glide and off-glide are also sometimes used to refer to the beginning and end of any sound, not necessarily a vowel, such as the approach and release phases of a plosive.)

Answer 2

The term "glide" is used to include [h,ʔ], but the laryngeal glides would not be called semivowels. If you consult the IPA chart, you will see that neither "glide" nor "semivowel" enter into that terminological standard. Using "semivowel" at all is mildly non-standard. The problem with asking about standards is that standards are "what people usually do, at this time", and they often change. The cited author's distinction is decidedly non-standard, although not hopeless. It provides a means of talking about the low-sonority element of diphthongs, which has plagued the profession for half a century.