The word "component" is a hugely overloaded term in the software development industry, but in this context a component is a grouping of related functionality encapsulated behind a well-defined interface. If you're using a language like Java or C#, the simplest way to think of a component is that it's a collection of implementation classes behind an interface. Aspects such as how those components are packaged (e.g. one component vs many components per JAR file, DLL, shared library, etc) is a separate and orthogonal concern.

An important point to note here is that all components inside a container typically execute in the same process space. In the C4 model, components are not separately deployable units.

An  Application Component is a functionnal unit of software (java class, COBOL Program, Batch) that is  a consistent, indivisible unit of processing of an Application producing and consuming its Information Outcome Events though APIs (Application Interface).

a)  Application Components are assembled and orchestrated in Applications.

b)  Application Components cannot be directly deployed to Computing Systems: they need to be organized in Deployable Application Packages.

 Application Component is a Micro enterprise asset that sits at the lowest level of Business Software System decomposition.

Example: the "Salary and Wage Calculation" component is an  Application Component that is part of the "Payroll" Application.

A  Deployable Data Package  represents a data part of an Application that must be hosted and accessed by application services (code) to run.

Each  Deployable Data Package is associated to Required Software Technologys (for data hosting and access) and can host several data structures.

Architect can also prescribes a kind of hosting artefact (IaaS/PaaS cloud service or IT server model).

A  Deployable Application Package  is a split of application code according to deployment criteria at runtime. For example, it may be Front End/Back End or GUI/Business Logic etc..

Each  Deployable Application Package is associated to required Software Technology(ies) (for running) and can host code of several Application Component.

Architects can also prescribe a kind of hosting artefact (IaaS/PaaS cloud service or IT server model).

An  Application Deployment Architecture describes one possible deployment configuration of an Application.

It contains Deployable Packages to host, prescribed type of hosting and required  Software Physical Channels (with communication protocols, port numbers...) to communicate with each other.

An  Application is a Business Software System that provides a set of  Functionality(ies) that End Users see as a single unit.

Essentially  Applications are architectural constructions resulting from the combinaison of the following four criteria:

1) A group of  Functionality that End Users see as a single unit.

2) A managed asset (Managed Application) associated with a budget line in the context of an Application Portfolio.

3) A body of code that is seen by developers as a single unit.

4) A group of deployable software units (Deployable Application Packages) that must be installed together on one or multiple execution nodes (Computing System).

 Application is a Mezzo enterprise asset  that sits between Application System and Application Component in the decomposition of Business Software Systems.

Example: " Payroll" is an  Application that is part an " HR System" which is an Application System.

The "Payroll"  Application includes, among other things, the "Salary and Wage Calculation" Application Component.