Dear Akhil, your confusion is quite natural because of the recurrence of the term "Industrial Establishment" in various chapters of the Industrial Disputes Act, 1947, with different meanings. However, you can certainly dispel this confusion with a little more effort by re-reading with reference to the context wherever it is used.
In common parlance, every establishment carrying on any activity pertaining to an industry is an industrial establishment. Such activities may include manufacturing, mining, exploration of oil and allied products, business/trading including buying and selling of goods and commodities, and rendering services like transportation of people and goods, telecommunications, hospitality, education, healthcare, entertainment, etc. Commercial activities like banking, non-banking financial activities, insurance, and so on are also included.
The complex nature of social life is such that every activity, irrespective of its nature and purpose, requires hiring the services of human beings for some reward, which can be either material or otherwise. Take, for example, the running of a temple or a church. It is essentially a religious activity aiming at spiritual benefits for its followers. However, such a religious institution/undertaking may engage in other activities too, like running lodging houses, transportation, renting out buildings, and selling religious artifacts and prasads on a large scale, which are analogous to trade or business. These can be separable from the main spiritual activity of the temple or church. Therefore, that particular separable activity is an industrial establishment. Similarly, if the predominant activity of the undertaking is analogous to industry and the other non-industrial activities of the undertaking are not separable, then the entire undertaking is an industrial establishment for the purpose of the ID Act, 1947. That is the exact purpose and meaning of the term "industrial establishment" as defined under section 2(ka) of the ID Act in Chapter I.
Chapter V-A of the Act deals with lay-off and retrenchment of certain workmen and closure of the establishment generally and specifically with reference to industrial establishments employing less than 100 workmen on average in a period of 12 months prior to lay-off/retrenchment/closure, as the case may be.
Here, the Act has to differentiate the establishments in terms of the application of this chapter as well as the prefixed number of workmen. Therefore, there is another definition of the term "industrial establishment" with an explanation of clarifying nature under section 25-A for the specific purposes of this chapter only. They are (1) those establishments to which Chapter V-B does not apply or such of the factory or mine or plantation where less than 50 workmen are/were employed or a seasonal establishment. For these establishments, no necessity for obtaining permission for lay-off or retrenchment or closure is necessary. Regarding compensation for lay-off in these establishments, I've already placed my view on record based on a case law supra. Insofar as compensation for retrenchment and closure, sections 25F and 25FFF have to be strictly followed.
Coming to all other industrial establishments employing 01 to 99 workmen, no permission is required for lay-off/retrenchment/closure. However, it is mandatory to pay compensations under sections 25-C, 25-F, and 25-FFF respectively. Besides, only in the case of closure, those establishments having 50 and above but below 100 workmen on their rolls must send a 60-day prior notice to the Government under section 25-FFA.
Here, by all other establishments, I mean every establishment employing less than 100 workmen other than those industrial establishments mentioned in section 25-A of Chapter V-A and even those establishments employing 100 and more workmen as well, other than those mentioned and defined in sections 25-K and 25-L respectively in Chapter V-B of the ID Act, 1947.
Regarding Chapter V-B, I need not explain in detail about the aspects of lay-off, retrenchment, and closure, for the concerned provisions are very clear and self-explanatory. However, you should remember that section 25-S of Chapter V-B mandates the application of the general provisions of sections 25B, 25D, 25FF, 25G, 25H, and 25J of Chapter V-A.