> ## Documentation Index > Fetch the complete documentation index at: https://docs.tavus.io/llms.txt > Use this file to discover all available pages before exploring further. # Overview > Define how your PAL behaves, responds, and speaks by configuring layers and pipeline modes. A **PAL** (Personified Application Layer) contains the full configuration for its role in CVI: behavior, knowledge, objectives, guardrails, tools, and every pipeline layer. The **face** defines the on-screen likeness and voice; the PAL defines how it thinks, speaks, and acts. **Terminology update:** Tavus now uses **PAL** (behavior, knowledge, and pipeline configuration) and **Face** (visual appearance and voice) in the API and docs. Legacy names **persona** and **replica** still work on existing endpoints and request fields (`/v2/personas`, `/v2/replicas`, `persona_id`, `replica_id`, and related aliases) for backward compatibility. **At a glance** * **PAL** - The agent's identity (name, behavior) plus **pipeline mode**, **default face**, **layers**, **documents** (Knowledge Base), **objectives**, and **guardrails**. Voice comes from the **face** by default; the TTS layer can override it. * **Relationship to CVI** - PALs hold the settings that drive a real-time CVI session; see **[What is CVI?](/sections/conversational-video-interface/overview-cvi)** for the full stack (WebRTC, layers, Phoenix, and latency characteristics on the default path). * **Layers (order of guides below)** - Perception → STT → Conversational Flow → LLM → TTS; each has its own configuration page. ## PAL Customization Options Each PAL includes configurable fields. Here's what you can customize: * **PAL Name**: Display name shown when the PAL joins a call. * **System Prompt**: Instructions sent to the language model to shape the PAL's tone, personality, and behavior. * **Pipeline mode**: Controls which CVI pipeline layers are active and how input/output flows through the system. See [Pipeline modes](/sections/conversational-video-interface/quickstart/pipeline-modes) for how the full pipeline, Echo, integrations, and custom LLM paths differ. * **Default face**: Sets the photorealistic face associated with the PAL (`default_face_id` on `POST /v2/pals`; required). * **Layers**: Perception, STT, conversational flow, LLM, and TTS - each processes part of the interaction and can be tuned independently (see [Layers](#layers) below). * **Documents**: A set of documents that the PAL has access to via the **Knowledge Base** (retrieval-augmented generation, RAG). * **Objectives**: The goal-oriented instructions your PAL will adhere to throughout the conversation. * **Guardrails**: Conversational boundaries that can be used to strictly enforce desired behavior. ## Objectives & Guardrails Provide your PAL with robust workflow management tools, curated to your use case The sequence of goals your PAL will work to achieve throughout the conversation - for example, gathering a piece of information from the user. Conversational boundaries that can be used to strictly enforce desired behavior. ## Layers Explore our in-depth guides to customize each layer to fit your specific use case: Defines how the PAL interprets visual input like facial expressions and gestures. Transcribes user speech into text using the configured speech-to-text engine. Controls turn-taking, interruption handling, and active listening behavior for natural conversations. Generates PAL responses using a language model. Supports Tavus-hosted or custom LLMs. Converts text responses into speech using Tavus or supported third-party TTS engines. Gives the PAL an email identity so it can be invited to Google Meet calls via Google Calendar and join automatically - including meetings already in progress.