# From Lean Production to Lean 4.0: A Systematic Literature Review with a Historical Perspective
## 3 Results
### Answering RQ3. Historical Evolution of the Term \"Lean\"  
As already pointed out, the expression \"lean production system\" was coined by [PERSON] in 1988 [23]. The seminal and best-selling book, _The Machine that Changed the World_[21], popularized the term \"lean production\"; and earlier similar expressions were completely abandoned (with the only exception being just-in-time, which survived in the supply chain literature until now).  
[PERSON] et al. [21] used the term \"lean production\" in contrast to \"mass production\" with the intentions of setting a benchmark, although the original systemic vision was lost. This is probably the first symptom of the \"lack of distinction between the systems and its components\" as [PERSON] et al. [6] suggested.  
Thus, 1990 can be considered the year when the term \"lean\" became popularized as an operations management concept. From 1990 to 1995, the term \"lean\" was adopted in the literature mainly as \"lean production\". The first research papers focused on either supporting or questioning lean [40; 41; 42] while describing the first lean experiences and the limits of this practice [42].  
In 1991, [PERSON] et al. [43] introduced \"lean manufacturing\" as a synonym for \"lean production\", and this term became more popular after 2000. Nowadays, \"lean manufacturing\" is the preferred expression for referring to lean in industrial operations (Figure 5).  
From 1992 to 1996, some authors intended to upgrade lean to a more conceptual level by introducing the terms \"lean management\", \"lean enterprise\" [44], and \"lean thinking\" [45]. This opened the door to using the term in non-manufacturing contexts, such as the services sector.  
In parallel, the period 1994 to 2000 saw the first attempts to apply lean to different production contexts (lean construction) as well as to others outside pure production (lean logistics, lean supply chain) or by combining it with supplementary topics (lean and green, lean product, lean six sigma). The fragmentation of the lean system into its tools continued with books such as _Lean Toolbox_[46]  
It was not until 2005 that the lean concept opened its scope to the services sector, mainly under the umbrella of lean six sigma, lean office, lean healthcare/hospital, and, recently, lean startup.  
Finally, in 2017, lean 4.0 appeared as a promising way for new developments by fusing lean and Industry 4.0 technologies.  
All in all, the term \"lean\", which was initially conceptualized as a \"lean production system\", has evolved from 1988 to 2020 as a \"living concept\". This evolution can be ascribed to the following proposed mechanisms that mostly combined with each other over time:  
* Expansion: extending the concept in the operations field.
* Transfer: applying the concept beyond production.
* Targeting: focusing the concept on a particular sector.
* Combination: merging the concept with other concepts.  
Through analyses of the scientific literature, this work has identified the most important lean specifiers (\"surmames\"). They are presented in chronological order of their appearance and describe (a) the first record found in our database analyses; (b) the historical trajectory based on the most relevant publications; (c) the evolution mechanisms; and (d) the present situation in terms of research interests. A chart with the yearly evolution of papers-per-year complements the summary.